Wednesday, July 07, 2004
Microsoft Interview Questions  1
1.
放飞技术网上面onefi整理的 Microsoft程序员测试题
一．最基本题型（说明：此类题型比较简单）
1.烧一根不均匀的绳，从头烧到尾总共需要1个小时。现在有若干条材质相同的绳子，问如何用烧绳的方法来计时一个小时十五分钟呢？（答案：一根从两头烧 ，并且同是从中间任何一处开始烧。烧完后即为十五分钟。然后再烧一根就是一个小时。）
2.你有一桶果冻，其中有黄色、绿色、红色三种，闭上眼睛抓取同种颜色的两个。抓取多少个就可以确定你肯定有两个同一颜色的果冻？（5秒1分钟）
3.如果你有无穷多的水，一个3公升的提捅，一个5公升的提捅，两只提捅形状上下都不均匀，问你如何才能准确称出4公升的水？（40秒3分钟）
4.一个岔路口分别通向诚实国和说谎国。来了两个人，已知一个是诚实国的，另一个是说谎国的。诚实国永远说实话，说谎国永远说谎话。现在你要去说谎国，但不知道应该走哪条路，需要问这两个人。请问应该怎么问？（20秒2分钟）
5.12个球一个天平，现知道只有一个和其它的重量不同，问怎样称才能用三次就找到那个球。13个呢？（注意此题并未说明那个球的重量是轻是重，所以需要仔细考虑）（5分钟1小时）
6.在9个点上画10条直线，要求每条直线上至少有三个点？（3分钟20分钟）
7.在一天的24小时之中，时钟的时针、分针和秒针完全重合在一起的时候有几次？都分别是什么时间？你怎样算出来的？（5分钟15分钟）
二．没有答案型（说明：这些题显然不是考你智力。而考的是你的反应能力。这种题大多数没有答案，但是要看你的反应喽！）
1.为什么下水道的盖子是圆的？
2.中国有多少辆汽车？
3.将汽车钥匙插入车门，向哪个方向旋转就可以打开车锁？ （按：好在我坐了N次同学的车买菜）
4.如果你要去掉中国的34个省（含自治区、直辖市和港澳特区及台湾省）中的任何一个，你会去掉哪一个，为什么？
5.多少个加油站才能满足中国的所有汽车？
6.想象你站在镜子前，请问，为什么镜子中的影象可以颠倒左右，却不能颠倒上下？
7.为什么在任何旅馆里，你打开热水，热水都会瞬间倾泻而出？
8.你怎样将Excel的用法解释给你的奶奶听？
9.你怎样重新改进和设计一个ATM银行自动取款机？
10.如果你不得不重新学习一种新的计算机语言，你打算怎样着手来开始？
11.如果你的生涯规划中打算在5年内受到奖励，那获取该项奖励的动机是什么？观众是谁？
12.如果微软告诉你，我们打算投资五百万美元来启动你的投资计划，你将开始什么样商业计划？为什么？
13.如果你能够将全世界的电脑厂商集合在一个办公室里，然后告诉他们将被强迫做一件事，那件事将是什么？
三．难题（说明：这类题有一定难度，如果得不到答案，也不能说明什么。如果你想到了解题思路，那么答案马上就能出来。如果想不到思路，那么……就别想解出来了。）
1.你让工人为你工作7天，回报是一根金条，这个金条平分成相连的7段，你必须在每天结束的时候给他们一段金条。如果只允许你两次把金条弄断，你如何给你的工人付费？
2.有一辆火车以每小时15公里的速度离开北京直奔广州，同时另一辆火车每小时20公里的速度从广州开往北京。如果有一只鸟，以30公里每小时的速度和两辆火车同时启动，从北京出发，碰到另一辆车后就向相反的方向返回去飞，就这样依次在两辆火车之间来回地飞，直到两辆火车相遇。请问，这只鸟共飞行了多长的距离？
3.你有四个装药丸的罐子，每个药丸都有一定的重量，被污染的药丸是没被污染的药丸的重量+1。只称量一次，如何判断哪个罐子的药被污染了？
4.门外三个开关分别对应室内三盏灯，线路良好，在门外控制开关时候不能看到室内灯的情况，现在只允许进门一次，确定开关和灯的对应关系？
5.人民币为什么只有1、2、5、10的面值？
6.你有两个罐子以及50个红色弹球和50个蓝色弹球，随机选出一个罐子， 随机选出一个弹球放入罐子，怎么给出红色弹球最大的选中机会？在你的计划里，得到红球的几率是多少？
四．超难题（说明：如果你是第一次看到这种题，并且以前从来没有见过类似的题型，并且能够在半个小时之内做出答案。只能说明你的智力超常……）
第一题 . 五个海盗抢到了100颗宝石，每一颗都一样大小和价值连城。他们决定这么分：
抽签决定自己的号码（1、2、3、4、5）
首先，由1号提出分配方案，然后大家表决，当且仅当超过半数的人同意时，按照他的方案进行分配，否则将被扔进大海喂鲨鱼
如果1号死后，再由2号提出分配方案，然后剩下的4人进行表决，当且仅当超过半数的人同意时，按照他的方案进行分配，否则将被扔入大海喂鲨鱼
依此类推
条件：每个海盗都是很聪明的人，都能很理智地做出判断，从而做出选择。
问题：第一个海盗提出怎样的分配方案才能使自己的收益最大化？
第二题 . 一道关于飞机加油的问题，已知：
每个飞机只有一个油箱，
飞机之间可以相互加油（注意是相互，没有加油机）
一箱油可供一架飞机绕地球飞半圈，
问题：
为使至少一架飞机绕地球一圈回到起飞时的飞机场，至少需要出动几架飞机？（所有飞机从同一机场起飞，而且必须安全返回机场，不允许中途降落，中间没有飞机场）
五．主观题（说明：在以后的工作过程中，我们可定会犯这样那样的错误。既然错误已经酿成，损失在所难免，我们只能想办法把损失减少到最小。如果能巧妙地回答出这些问题，再发生错误的情况下。能让客户有最少的抱怨，公司有最少的损失。）
1.某手机厂家由于设计失误，有可能造成电池寿命比原来设计的寿命短一半（不是冲放电时间），解决方案就是免费更换电池或给50元购买该厂家新手机的折换券。请给所有已购买的用户写信告诉解决方案。
2.一高层领导在参观某博物馆时，向博物馆馆员小王要了一块明代的城砖作为纪念，按国家规定，任何人不得将博物馆收藏品变为私有。博物馆馆长需要如何写信给这位领导，将城砖取回。
3.营业员小姐由于工作失误，将2万元的笔记本电脑以1.2万元错卖给李先生，王小姐的经理怎么写信给李先生试图将钱要回来？
六.算法题（说明：这些题就不是什么花样了，考的是你的基础知识怎么样。再聪明而没有实学的人都将会被这些题所淘汰。）
1.链表和数组的区别在哪里？
2.编写实现链表排序的一种算法。说明为什么你会选择用这样的方法？
3.编写实现数组排序的一种算法。说明为什么你会选择用这样的方法？
4.请编写能直接实现strstr()函数功能的代码。
5.编写反转字符串的程序，要求优化速度、优化空间。
6.在链表里如何发现循环链接？
7.给出洗牌的一个算法，并将洗好的牌存储在一个整形数组里。
8.写一个函数，检查字符是否是整数，如果是，返回其整数值。（或者：怎样只用4行代码编写出一个从字符串到长整形的函数？）
9.给出一个函数来输出一个字符串的所有排列。
10.请编写实现malloc()内存分配函数功能一样的代码。
11.给出一个函数来复制两个字符串A和B。字符串A的后几个字节和字符串B的前几个字节重叠。
12.怎样编写一个程序，把一个有序整数数组放到二叉树中？
13.怎样从顶部开始逐层打印二叉树结点数据？请编程。
14.怎样把一个链表掉个顺序（也就是反序，注意链表的边界条件并考虑空链表）？
2.
Three Microsoft Interview Questions
From http://blog.csdn.net/csumck/archive/2004/11/01/162121.aspx
http://blog.csdn.net/linweixuan/archive/2004/09/28/littlebigendian.aspx
1）实现string toHex(int)把一个十进制转换成十六进制。（完全用算法实现）
第一个题目很简单，就是用十进制数不停的除以16，将所有的余数累加起来便是结果。我用C++简单的实现了一下，下面是代码（VC++.NET/windows xp）：
#include
#include
using namespace std;
string ToHex(int dec)
{
unsigned int udec = (dec>=0)?(dec):(dec), yushu;
int pos = 8;
char Hex[11];
memset(Hex, '0', 9);
Hex[9] = 'H';
Hex[10] = '\0';
do//求余数
{
yushu = udec%16;
Hex[pos] = (yushu>9)?(yushu+55):(yushu+48);
udec = udec/16;
}
while (udec!=0);
if (Hex[pos+1]>64)//如果最高位是字母，则字符串前面补0
Hex[pos] = '0';
else
++pos;
if (dec<0)//如果是负数，在前面加负号
Hex[pos] = '';
return (string(Hex+pos));
2）实现一个计算大位数（如100位以上）相乘结果的函数string multiply(sting,string)。（请完全用算法实现）
第二个题目挺复杂的，大位数的乘法是不能使用atoi将字符串化为整型在相乘的，那样会溢出。模拟手算也不太可能，因为手算的话需要大量的内存记录中间结果。
我想到的比较好的方法是模拟计算机中的乘法。我这个学期刚刚学的计算机组成原理里有讲到关于计算机中原码一位乘法的实现。关于这种方法的具体内容大家可以很容易的在网上找到。使用这种方法计算n位数乘法的话只需2n+2位的缓冲。但是实现起来挺麻烦的，真的行不行我心里也没底。我只是阐述一下我的看法，大家有什么看法欢迎讨论。
那个帖子有牛人给出了C++实现，抄记于下（我都不敢看，太长）：
xiao_wang(小王)
#include "stdafx.h"
#include
#include
using namespace std;
class slong
{
public:
slong()
{
_str = "";
}
slong(string str)
{
string::iterator itor = str.begin();
for(; itor != str.end(); ++itor)
{
if(*itor < '0'  *itor > '9')
throw "the parameter is error.";
}
_str = str;
}
slong(char* s)
{
if(s == NULL)
{
_str = "";
return;
}
size_t size = strlen(s);
for(size_t i = 0; i < size; ++i)
{
if(s[i] < '0'  s[i] > '9')
throw "the parameter is error.";
}
_str = s;
}
slong(const slong& sl)
{
_str = sl._str;
}
slong& operator =(const slong& sl)
{
if(&sl == this)
return *this;
_str = sl._str;
return *this;
}
slong operator *(slong& sl)
{
if(sl._str.length() == 0)
return *this;
int n = static_cast(sl._str.length());
int m = static_cast(this>_str.length());
int t = m + n  1; // caculate times
string::reverse_iterator itor1, itor2;
int j = 0;
int k = 0;
int c = 0;
int r = 0;
int v = 0;
char s[2];
string rproduct;
for(int i = 0; i < t; ++i)
{
v = 0;
j = 0;
itor1 = _str.rbegin();
for(; itor1 != _str.rend(); ++itor1)
{
k = 0;
itor2 = sl._str.rbegin();
for(; itor2 != sl._str.rend(); ++itor2)
{
if(j + k == i)
{
v += ctoi(*itor1) * ctoi(*itor2);
break;
}
k++;
}
j++;
if(j > i)
break;
}
v += c;
r = v%10;
c = v/10;
itoa(r, s, 10);
rproduct += s;
}
if(c != 0)
{
itoa(c, s, 10);
rproduct += s;
}
string temp;
temp.resize(product.length());
string::reverse_iterator ritor = product.rbegin();
string::iterator itor = temp.begin();
for(; itor != temp.end(); ++itor)
{
*itor = *ritor;
ritor++;
}
slong product(temp);
return product;
}
int ctoi(char c)
{
return c  48;
}
string value()
{
return _str;
}
private:
string _str;
};
int _tmain(int argc, _TCHAR* argv[])
{
string s1, s2;
cout << "please input first operator" << endl;
cin >> s1;
cout << "please input second operator" << endl;
cin >> s2;
slong sl1(s1);
slong sl2(s2);
slong sl3 = sl1 * sl2;
cout << "the value is :" << endl;
cout << sl3.value() << endl;
char word;
while(cin >> word)
if(word == 'q')
break;
return 0;
}
3) 编写函数判断计算机的字节存储顺序是升序（little endian）还是是降序（bigdian）
1在32位计算机升序排列为
0000 0000 0000 0001 0000 0000 0000 0000
降序为
0000 0000 0000 0000 0000 0000 0000 0001
这个问题应该可以用指针解决。
int i = 1;
char* pc = (char*)(&i);
pc++;
if (*pc > 0) 升序; else 降序;
又看到了一种做法，摘抄于下：
//作者：sutra(只回答经典问题 只提供经典答案)
bool is_little_endian()
{
union {
int i ;
char c ;
} uIc ;
uIc.i = 1 ;
return (uIc.c != 0) ;
}
另一段来自linweixuan得代码
如何判断机器的大小端的问题,在阅读ORBacus的代码中看到的，特此载出
3.1.
int
main ()
{
/* Are we little or big endian? From Harbison&Steele. */
union
{
long l;
char c[sizeof (long)];
} u;
u.l = 1;
exit (u.c[sizeof (long)  1] == 1);
}
3.2.
#include
#include
int
main ()
{
#if BYTE_ORDER != BIG_ENDIAN
not big endian
#endif
;
return 0;
}
3.3.
#include
#include
int
main ()
{
#if !BYTE_ORDER  !BIG_ENDIAN  !LITTLE_ENDIAN
bogus endian macros
#endif
;
return 0;
}
3.
Interview Questions  Microsoft, etc.
From http://halcyon.usc.edu/~kiran/msqs.html
Disclaimer: This page is in no way connected with Microsoft Corporation, its affiliates, friends or haters
What?
Here is a set of questions that I have with me which software guys have asked at interviews in the past, most of them are actually from Microsoft but a few have been pulled together from other places too. I have collected these from friends and would welcome any additions from you. Mail them to kiran AT usc DOT edu. Do send me your solutions, but the intent of this page is to kindle enough interest in you to try similar logic and programming questions.
PLEASE DO NOT REQUEST ME FOR MORE SOLUTIONS!
Why?
I have grown up reading Martin Gardner's Scientific American columns on Mathematical Games and interesting mathematics olympiad problems in high school. I discovered, to my delight, Bentley's Programming Pearls and David Gries' The Science of Programming in my computer science education. There is underlying beauty in mathematics and computer science. Some find it and others hate the subjects. When I found some of the Microsoft interview questions in graduate school, they were similar to mathematical puzzles that I was interested in. I started collecting them more as an illustration of interesting logic puzzles and algorithms in programming, than as an interview aid. If it has morphed into an interview questions page, that is more due to interest from all interviewees out there.
Some of the programming questions have a basic foundation in mathematics and algorithms. If the given data structure has a specific amount of information and the question asks you to extract/modify the given information, it is possible (though not always obvious) to find optimal solutions, and prove that it cannot be done any better, by quantifying the information content. But, there are always elegant and ugly ways to extract the same information. When you manage to find out the optimal solution to a problem, it usually not only turns out to be elegant, but also has the "aha!" factor to it. Try proving on paper the following question from my undergraduate midterm:
1. Everyone Loves All Lovers
2. Romeo Loves Juliet
Therefore, prove (i.e. 1 AND 2 => 3)
3. I Love You
How?
To answer one of the more frequent questions that I get: No! I have never interviewed at Microsoft. In fact, I work in a microprocessor company far removed from any software development (though I work mostly in programming). However, I have had two of my roommates and two more housemates eventually working in Microsoft, in addition to a large number of friends. None of them have contributed to this page AFTER they started working at Microsoft. Microsoft itself does not hold any patents and nor has it invented most of the questions. Most of them come from mathematics and physics books, party puzzles, programming lore and standard textbooks. I know many companies ask similar questions, though Microsoft might have made the practice more common (especially with the manhole cover type of questions).
Usage
I have spent some time in collecting with the intention of their value as a practice session. They are not meant to be exact questions that you need to know and answer in an interview. They are supposed to make you think! Discuss with your friends, colleagues, professors for answers (get your tuition money's worth). I have left the page in simple text format so you can print them out and try them on your flight to the interview in case you are pressed for time. One of the strangest phone calls I remember is from a girl, staying up in a Microsoft provided hotel room in Redmond the night before the interview, asking me about the solution for one of the questions from this page. I hope the rest of you are saner (or do not have my phone number).
Kiran Bondalapati
Ze Meat
Puzzles, Riddles, etc.
Programming Questions
Computer Networks, Databases, etc.
Computer Architecture
Puzzles, Riddles and Others
0. Classic: If a bear walks one mile south, turns left and walks one mile to the east and then turns left again and walks one mile north and arrives at its original position, what is the color of the bear.
ANS. The color of the bear is trivial. The possible solutions to it are interesting. In addition to the trivial north pole, there are additional circles near south pole. Think it out.
* 1. Given a rectangular (cuboidal for the puritans) cake with a rectangular piece removed (any size or orientation), how would you cut the remainder of the cake into two equal halves with one straight cut of a knife?
ANS. Join the centers of the original and the removed rectangle. It works for cuboids too! BTW, I have been getting many questions asking why a horizontal slice across the middle will not do. Please note the "any size or orientation" in the question! Don't get boxed in by the way you cut your birthday cake :) Think out of the box.
2. There are 3 baskets. one of them have apples, one has oranges only and the other has mixture of apples and oranges. The labels on their baskets always lie. (i.e. if the label says oranges, you are sure that it doesn't have oranges only,it could be a mixture) The task is to pick one basket and pick only one fruit from it and then correctly label all the three baskets.
HINT. There are only two combinations of distributions in which ALL the baskets have wrong labels. By picking a fruit from the one labeled MIXTURE, it is possible to tell what the other two baskets have.
3. You have 8 balls. One of them is defective and weighs less than others. You have a balance to measure balls against each other. In 2 weighings how do you find the defective one?
4. Why is a manhole cover round?
HINT. The diagonal of a square hole is larger than the side of a cover!
Alternate answers: 1. Round covers can be transported by one person, because they can be rolled on their edge. 2. A round cover doesn't need to be rotated to fit over a hole.
5. How many cars are there in the USA?
6. You've got someone working for you for seven days and a gold bar to pay them. The gold bar is segmented into seven connected pieces. You must give them a piece of gold at the end of every day. If you are only allowed to make two breaks in the gold bar, how do you pay your worker?
7. One train leaves Los Angeles at 15mph heading for New York. Another train leaves from New York at 20mph heading for Los Angeles on the same track. If a bird, flying at 25mph, leaves from Los Angeles at the same time as the train and flies back and forth between the two trains until they collide, how far will the bird have traveled?
HINT. Think relative speed of the trains.
8. You have two jars, 50 red marbles and 50 blue marbles. A jar will be picked at random, and then a marble will be picked from the jar. Placing all of the marbles in the jars, how can you maximize the chances of a red marble being picked? What are the exact odds of getting a red marble using your scheme?
9. Imagine you are standing in front of a mirror, facing it. Raise your left hand. Raise your right hand. Look at your reflection. When you raise your left hand your reflection raises what appears to be his right hand. But when you tilt your head up, your reflection does too, and does not appear to tilt his/her head down. Why is it that the mirror appears to reverse left and right, but not up and down?
10. You have 5 jars of pills. Each pill weighs 10 gram, except for contaminated pills contained in one jar, where each pill weighs 9 gm. Given a scale, how could you tell which jar had the contaminated pills in just one measurement?
ANS. 1. Mark the jars with numbers 1, 2, 3, 4, and 5.
2. Take 1 pill from jar 1, take 2 pills from jar 2, take 3 pills from jar 3, take 4 pills from jar 4 and take 5 pills from jar 5.
3. Put all of them on the scale at once and take the measurement.
4. Now, subtract the measurement from 150 ( 1*10 + 2*10 + 3*10 + 4*10 + 5*10)
5. The result will give you the jar number which has contaminated pill.
11. If you had an infinite supply of water and a 5 quart and 3 quart pail, how would you measure exactly 4 quarts?
12. You have a bucket of jelly beans. Some are red, some are blue, and some green. With your eyes closed, pick out 2 of a like color. How many do you have to grab to be sure you have 2 of the same?
13. Which way should the key turn in a car door to unlock it?
14. If you could remove any of the 50 states, which state would it be and why?
15. There are four dogs/ants/people at four corners of a square of unit distance. At the same instant all of them start running with unit speed towards the person on their clockwise direction and will always run towards that target. How long does it take for them to meet and where?
HINT. They will meet in the center and the distance covered by them is independent of the path they actually take (a spiral).
16. (from Tara Hovel) A helicopter drops two trains, each on a parachute, onto a straight infinite railway line. There is an undefined distance between the two trains. Each faces the same direction, and upon landing, the parachute attached to each train falls to the ground next to the train and detaches. Each train has a microchip that controls its motion. The chips are identical. There is no way for the trains to know where they are. You need to write the code in the chip to make the trains bump into each other. Each line of code takes a single clock cycle to execute.
You can use the following commands (and only these);
MF  moves the train forward
MB  moves the train backward
IF (P)  conditional that's satisfied if the train is next to a parachute. There is no "then" to this IF statement.
GOTO
ANS.
A: MF
IF (P)
GOTO B
GOTO A

B: MF
GOTO B
Explanation: The first line simply gets them off the parachutes. You need to get the trains off their parachutes so the back train can find the front train's parachute, creating a special condition that will allow it to break out of the code they both have to follow initially. They both loop through A: until the back train finds the front train's parachute, at which point it goes to B: and gets stuck in that loop. The front train still hasn't found a parachute, so it keeps in the A loop. Because each line of code takes a "clock cycle" to execute, it takes longer to execute the A loop than the B loop, therefore the back train (running in the B loop) will catch up to the front train.
Personality
It is best to read some website or a book for questions like these.
1. Tell me the courses you liked and why did you like them.
2. Give an instance in your life in which you were faced with a problem and you tackled it successfully.
3. What is your ideal working environment.
4. Why do you think you are smart.
5. Questions on the projects listed on the Resume.
6. Do you want to know any thing about the company.( Try to ask some relevant and interesting question).
7. How long do you want to stay in USA and why (I guess noncitizens get this)?
8. What is your geographical preference?
9. What are your expectations from the job.

Algorithms and Programming
1. Given a rectangular (cuboidal for the puritans) cake with a rectangular piece removed (any size or orientation), how would you cut the remainder of the cake into two equal halves with one straight cut of a knife ?
2. You're given an array containing both positive and negative integers and required to find the subarray with the largest sum (O(N) a la KBL). Write a routine in C for the above.
3. Given an array of size N in which every number is between 1 and N, determine if there are any duplicates in it. You are allowed to destroy the array if you like. [ I ended up giving about 4 or 5 different solutions for this, each supposedly better than the others ].
4. Write a routine to draw a circle (x ** 2 + y ** 2 = r ** 2) without making use of any floating point computations at all. [ This one had me stuck for quite some time and I first gave a solution that did have floating point computations ].
5. Given only putchar (no sprintf, itoa, etc.) write a routine putlong that prints out an unsigned long in decimal. [ I gave the obvious solution of taking % 10 and / 10, which gives us the decimal value in reverse order. This requires an array since we need to print it out in the correct order. The interviewer wasn't too pleased and asked me to give a solution which didn't need the array ].
6. Give a oneline C expression to test whether a number is a power of 2. [No loops allowed  it's a simple test.]
7. Given an array of characters which form a sentence of words, give an efficient algorithm to reverse the order of the words (not characters) in it.
8. How many points are there on the globe where by walking one mile south, one mile east and one mile north you reach the place where you started.
9. Give a very good method to count the number of ones in a "n" (e.g. 32) bit number.
ANS. Given below are simple solutions, find a solution that does it in log (n) steps.
Iterative
function iterativecount (unsigned int n)
begin
int count=0;
while (n)
begin
count += n & 0x1 ;
n >>= 1;
end
return count;
end
Sparse Count
function sparsecount (unsigned int n)
begin
int count=0;
while (n)
begin
count++;
n &= (n1);
end
return count ;
end
10. What are the different ways to implement a condition where the value of x can be either a 0 or a 1. Apparently the if then else solution has a jump when written out in assembly. if (x == 0) y=a else y=b There is a logical, arithmetic and a data structure solution to the above problem.
11. Reverse a linked list.
12. Insert in a sorted list
13. In a X's and 0's game (i.e. TIC TAC TOE) if you write a program for this give a fast way to generate the moves by the computer. I mean this should be the fastest way possible.
The answer is that you need to store all possible configurations of the board and the move that is associated with that. Then it boils down to just accessing the right element and getting the corresponding move for it. Do some analysis and do some more optimization in storage since otherwise it becomes infeasible to get the required storage in a DOS machine.
14. I was given two lines of assembly code which found the absolute value of a number stored in two's complement form. I had to recognize what the code was doing. Pretty simple if you know some assembly and some fundaes on number representation.
15. Give a fast way to multiply a number by 7.
16. How would go about finding out where to find a book in a library. (You don't know how exactly the books are organized beforehand).
17. Linked list manipulation.
18. Tradeoff between time spent in testing a product and getting into the market first.
19. What to test for given that there isn't enough time to test everything you want to.
20. First some definitions for this problem: a) An ASCII character is one byte long and the most significant bit in the byte is always '0'. b) A Kanji character is two bytes long. The only characteristic of a Kanji character is that in its first byte the most significant bit is '1'.
Now you are given an array of a characters (both ASCII and Kanji) and, an index into the array. The index points to the start of some character. Now you need to write a function to do a backspace (i.e. delete the character before the given index).
21. Delete an element from a doubly linked list.
22. Write a function to find the depth of a binary tree.
23. Given two strings S1 and S2. Delete from S2 all those characters which occur in S1 also and finally create a clean S2 with the relevant characters deleted.
24. Assuming that locks are the only reason due to which deadlocks can occur in a system. What would be a foolproof method of avoiding deadlocks in the system.
25. Reverse a linked list.
Ans: Possible answers 
iterative loop
curr>next = prev;
prev = curr;
curr = next;
next = curr>next
endloop
recursive reverse(ptr)
if (ptr>next == NULL)
return ptr;
temp = reverse(ptr>next);
temp>next = ptr;
return ptr;
end
26. Write a small lexical analyzer  interviewer gave tokens. expressions like "a*b" etc.
27. Besides communication cost, what is the other source of inefficiency in RPC? (answer : context switches, excessive buffer copying). How can you optimize the communication? (ans : communicate through shared memory on same machine, bypassing the kernel _ A Univ. of Wash. thesis)
28. Write a routine that prints out a 2D array in spiral order!
29. How is the readerswriters problem solved?  using semaphores/ada .. etc.
30. Ways of optimizing symbol table storage in compilers.
31. A walkthrough through the symbol table functions, lookup() implementation etc.  The interviewer was on the Microsoft C team.
32. A version of the "There are three persons X Y Z, one of which always lies".. etc..
33. There are 3 ants at 3 corners of a triangle, they randomly start moving towards another corner.. what is the probability that they don't collide.
34. Write an efficient algorithm and C code to shuffle a pack of cards.. this one was a feedback process until we came up with one with no extra storage.
35. The if (x == 0) y = 0 etc..
36. Some more bitwise optimization at assembly level
37. Some general questions on Lex, Yacc etc.
38. Given an array t[100] which contains numbers between 1..99. Return the duplicated value. Try both O(n) and O(nsquare).
39. Given an array of characters. How would you reverse it. ? How would you reverse it without using indexing in the array.
40. Given a sequence of characters. How will you convert the lower case characters to upper case characters. ( Try using bit vector  solutions given in the C lib typec.h)
41. Fundamentals of RPC.
42. Given a linked list which is sorted. How will u insert in sorted way.
43. Given a linked list How will you reverse it.
44. Give a good data structure for having n queues ( n not fixed) in a finite memory segment. You can have some datastructure separate for each queue. Try to use at least 90% of the memory space.
45. Do a breadth first traversal of a tree.
46. Write code for reversing a linked list.
47. Write, efficient code for extracting unique elements from a sorted list of array. e.g. (1, 1, 3, 3, 3, 5, 5, 5, 9, 9, 9, 9) > (1, 3, 5, 9).
48. Given an array of integers, find the contiguous subarray with the largest sum.
ANS. Can be done in O(n) time and O(1) extra space. Scan array from 1 to n. Remember the best subarray seen so far and the best subarray ending in i.
49. Given an array of length N containing integers between 1 and N, determine if it contains any duplicates.
ANS. [Is there an O(n) time solution that uses only O(1) extra space and does not destroy the original array?]
50. Sort an array of size n containing integers between 1 and K, given a temporary scratch integer array of size K.
ANS. Compute cumulative counts of integers in the auxiliary array. Now scan the original array, rotating cycles! [Can someone word this more nicely?]
* 51. An array of size k contains integers between 1 and n. You are given an additional scratch array of size n. Compress the original array by removing duplicates in it. What if k << n?
ANS. Can be done in O(k) time i.e. without initializing the auxiliary array!
52. An array of integers. The sum of the array is known not to overflow an integer. Compute the sum. What if we know that integers are in 2's complement form?
ANS. If numbers are in 2's complement, an ordinary looking loop like for(i=total=0;i< n;total+=array[i++]); will do. No need to check for overflows!
53. An array of characters. Reverse the order of words in it.
ANS. Write a routine to reverse a character array. Now call it for the given array and for each word in it.
* 54. An array of integers of size n. Generate a random permutation of the array, given a function rand_n() that returns an integer between 1 and n, both inclusive, with equal probability. What is the expected time of your algorithm?
ANS. "Expected time" should ring a bell. To compute a random permutation, use the standard algorithm of scanning array from n downto 1, swapping ith element with a uniformly random element <= ith. To compute a uniformly random integer between 1 and k (k < n), call rand_n() repeatedly until it returns a value in the desired range.
55. An array of pointers to (very long) strings. Find pointers to the (lexicographically) smallest and largest strings.
ANS. Scan array in pairs. Remember largestsofar and smallestsofar. Compare the larger of the two strings in the current pair with largestsofar to update it. And the smaller of the current pair with the smallestsofar to update it. For a total of <= 3n/2 strcmp() calls. That's also the lower bound.
56. Write a program to remove duplicates from a sorted array.
ANS. int remove_duplicates(int * p, int size)
{
int current, insert = 1;
for (current=1; current < size; current++)
if (p[current] != p[insert1])
{
p[insert] = p[current];
current++;
insert++;
} else
current++;
return insert;
}
57. C++ ( what is virtual function ? what happens if an error occurs in constructor or destructor. Discussion on error handling, templates, unique features of C++. What is different in C++, ( compare with unix).
58. Given a list of numbers ( fixed list) Now given any other list, how can you efficiently find out if there is any element in the second list that is an element of the first list (fixed list).
59. Given 3 lines of assembly code : find it is doing. IT was to find absolute value.
60. If you are on a boat and you throw out a suitcase, Will the level of water increase.
61. Print an integer using only putchar. Try doing it without using extra storage.
62. Write C code for (a) deleting an element from a linked list (b) traversing a linked list
63. What are various problems unique to distributed databases
64. Declare a void pointer ANS. void *ptr;
65. Make the pointer aligned to a 4 byte boundary in a efficient manner ANS. Assign the pointer to a long number and the number with 11...1100 add 4 to the number
66. What is a far pointer (in DOS)
67. What is a balanced tree
68. Given a linked list with the following property node2 is left child of node1, if node2 < node1 else, it is the right child.
O P


O A


O B


O C
How do you convert the above linked list to the form without disturbing the property. Write C code for that.
O P


O B
/ / / O ? O ?
determine where do A and C go
69. Describe the file system layout in the UNIX OS
ANS. describe boot block, super block, inodes and data layout
70. In UNIX, are the files allocated contiguous blocks of data
ANS. no, they might be fragmented
How is the fragmented data kept track of
ANS. Describe the direct blocks and indirect blocks in UNIX file system
71. Write an efficient C code for 'tr' program. 'tr' has two command line arguments. They both are strings of same length. tr reads an input file, replaces each character in the first string with the corresponding character in the second string. eg. 'tr abc xyz' replaces all 'a's by 'x's, 'b's by 'y's and so on. ANS.
a) have an array of length 26.
put 'x' in array element corr to 'a'
put 'y' in array element corr to 'b'
put 'z' in array element corr to 'c'
put 'd' in array element corr to 'd'
put 'e' in array element corr to 'e'
and so on.
the code
while (!eof)
{
c = getc();
putc(array[c  'a']);
}
72. what is disk interleaving
73. why is disk interleaving adopted
74. given a new disk, how do you determine which interleaving is the best a) give 1000 read operations with each kind of interleaving determine the best interleaving from the statistics
75. draw the graph with performance on one axis and 'n' on another, where 'n' in the 'n' in nway disk interleaving. (a tricky question, should be answered carefully)
76. I was a c++ code and was asked to find out the bug in that. The bug was that he declared an object locally in a function and tried to return the pointer to that object. Since the object is local to the function, it no more exists after returning from the function. The pointer, therefore, is invalid outside.
77. A real life problem  A square picture is cut into 16 squares and they are shuffled. Write a program to rearrange the 16 squares to get the original big square.
78.
int *a;
char *c;
*(a) = 20;
*c = *a;
printf("%c",*c);
what is the output?
79. Write a program to find whether a given m/c is bigendian or littleendian!
80. What is a volatile variable?
81. What is the scope of a static function in C ?
82. What is the difference between "malloc" and "calloc"?
83. struct n { int data; struct n* next}node;
node *c,*t;
c>data = 10;
t>next = null;
*c = *t;
what is the effect of the last statement?
84. If you're familiar with the ? operator x ? y : z
you want to implement that in a function: int cond(int x, int y, int z); using only ~, !, ^, &, +, , <<, >> no if statements, or loops or anything else, just those operators, and the function should correctly return y or z based on the value of x. You may use constants, but only 8 bit constants. You can cast all you want. You're not supposed to use extra variables, but in the end, it won't really matter, using vars just makes things cleaner. You should be able to reduce your solution to a single line in the end though that requires no extra vars.
85. You have an abstract computer, so just forget everything you know about computers, this one only does what I'm about to tell you it does. You can use as many variables as you need, there are no negative numbers, all numbers are integers. You do not know the size of the integers, they could be infinitely large, so you can't count on truncating at any point. There are NO comparisons allowed, no if statements or anything like that. There are only four operations you can do on a variable.
1) You can set a variable to 0.
2) You can set a variable = another variable.
3) You can increment a variable (only by 1), and it's a post increment.
4) You can loop. So, if you were to say loop(v1) and v1 = 10, your loop would execute 10 times, but the value in v1 wouldn't change so the first line in the loop can change value of v1 without changing the number of times you loop.
You need to do 3 things.
1) Write a function that decrements by 1.
2) Write a function that subtracts one variable from another.
3) Write a function that divides one variable by another.
4) See if you can implement all 3 using at most 4 variables. Meaning, you're not making function calls now, you're making macros. And at most you can have 4 variables. The restriction really only applies to divide, the other 2 are easy to do with 4 vars or less. Division on the other hand is dependent on the other 2 functions, so, if subtract requires 3 variables, then divide only has 1 variable left unchanged after a call to subtract. Basically, just make your function calls to decrement and subtract so you pass your vars in by reference, and you can't declare any new variables in a function, what you pass in is all it gets.
Linked lists
* 86. Under what circumstances can one delete an element from a singly linked list in constant time?
ANS. If the list is circular and there are no references to the nodes in the list from anywhere else! Just copy the contents of the next node and delete the next node. If the list is not circular, we can delete any but the last node using this idea. In that case, mark the last node as dummy!
* 87. Given a singly linked list, determine whether it contains a loop or not.
ANS. (a) Start reversing the list. If you reach the head, gotcha! there is a loop!
But this changes the list. So, reverse the list again.
(b) Maintain two pointers, initially pointing to the head. Advance one of them one node at a time. And the other one, two nodes at a time. If the latter overtakes the former at any time, there is a loop!
p1 = p2 = head;
do {
p1 = p1>next;
p2 = p2>next>next;
} while (p1 != p2);
88. Given a singly linked list, print out its contents in reverse order. Can you do it without using any extra space?
ANS. Start reversing the list. Do this again, printing the contents.
89. Given a binary tree with nodes, print out the values in preorder/inorder/postorder without using any extra space.
90. Reverse a singly linked list recursively. The function prototype is node * reverse (node *) ;
ANS.
node * reverse (node * n)
{
node * m ;
if (! (n && n > next))
return n ;
m = reverse (n > next) ;
n > next > next = n ;
n > next = NULL ;
return m ;
}
91. Given a singly linked list, find the middle of the list.
HINT. Use the single and double pointer jumping. Maintain two pointers, initially pointing to the head. Advance one of them one node at a time. And the other one, two nodes at a time. When the double reaches the end, the single is in the middle. This is not asymptotically faster but seems to take less steps than going through the list twice.
Bitmanipulation
92. Reverse the bits of an unsigned integer.
ANS.
#define reverse(x) (x=x>>16(0x0000ffff&x)<<16, x=(0xff00ff00&x)>>8(0x00ff00ff&x)<<8, x=(0xf0f0f0f0&x)>>4(0x0f0f0f0f&x)<<4, x=(0xcccccccc&x)>>2(0x33333333&x)<<2, x=(0xaaaaaaaa&x)>>1(0x55555555&x)<<1)
* 93. Compute the number of ones in an unsigned integer.
ANS.
#define count_ones(x) (x=(0xaaaaaaaa&x)>>1+(0x55555555&x), x=(0xcccccccc&x)>>2+(0x33333333&x), x=(0xf0f0f0f0&x)>>4+(0x0f0f0f0f&x), x=(0xff00ff00&x)>>8+(0x00ff00ff&x), x=x>>16+(0x0000ffff&x))
94. Compute the discrete log of an unsigned integer.
ANS.
#define discrete_log(h) (h=(h>>1)(h>>2), h=(h>>2), h=(h>>4), h=(h>>8), h=(h>>16), h=(0xaaaaaaaa&h)>>1+(0x55555555&h), h=(0xcccccccc&h)>>2+(0x33333333&h), h=(0xf0f0f0f0&h)>>4+(0x0f0f0f0f&h), h=(0xff00ff00&h)>>8+(0x00ff00ff&h), h=(h>>16)+(0x0000ffff&h))
If I understand it right, log2(2) =1, log2(3)=1, log2(4)=2..... But this macro does not work out log2(0) which does not exist! How do you think it should be handled?
* 95. How do we test most simply if an unsigned integer is a power of two?
ANS. #define power_of_two(x) \ ((x)&&(~(x&(x1))))
96. Set the highest significant bit of an unsigned integer to zero.
ANS. (from Denis Zabavchik) Set the highest significant bit of an unsigned integer to zero
#define zero_most_significant(h) \
(h&=(h>>1)(h>>2), \
h=(h>>2), \
h=(h>>4), \
h=(h>>8), \
h=(h>>16))
97. Let f(k) = y where k is the yth number in the increasing sequence of nonnegative integers with the same number of ones in its binary representation as y, e.g. f(0) = 1, f(1) = 1, f(2) = 2, f(3) = 1, f(4) = 3, f(5) = 2, f(6) = 3 and so on. Given k >= 0, compute f(k).
Others
98. A character set has 1 and 2 byte characters. One byte characters have 0 as the first bit. You just keep accumulating the characters in a buffer. Suppose at some point the user types a backspace, how can you remove the character efficiently. (Note: You cant store the last character typed because the user can type in arbitrarily many backspaces)
99. What is the simples way to check if the sum of two unsigned integers has resulted in an overflow.
100. How do you represent an nary tree? Write a program to print the nodes of such a tree in breadth first order.
101. Write the 'tr' program of UNIX. Invoked as
tr str1 str2. It reads stdin and prints it out to stdout, replacing every occurance of str1[i] with str2[i].
e.g. tr abc xyz
to be and not to be < input
to ye xnd not to ye < output

Networks and Security
1. How do you use RSA for both authentication and secrecy?
2. What is ARP and how does it work?
3. What's the difference between a switch and a router?
4. Name some routing protocols? (RIP,OSPF etc..)
5. How do you do authentication with message digest(MD5)? (Usually MD is used for finding tampering of data)
6. How do you implement a packet filter that distinguishes following cases and selects first case and rejects second case.
i) A host inside the corporate n/w makes a ftp request to outside host and the outside host sends reply.
ii) A host outside the network sends a ftp request to host inside. for the packet filter in both cases the source and destination fields will look the same.
7. How does traceroute work? Now how does traceroute make sure that the packet follows the same path that a previous (with ttl  1) probe packet went in?
8. Explain Kerberos Protocol ?
9. What are digital signatures and smart cards?
10. Difference between discretionary access control and mandatory access control?
Java
1. How do you find the size of a java object (not the primitive type) ?
ANS. type cast it to string and find its s.length()
2. Why is multiple inheritance not provided in Java?
3. Thread t = new Thread(); t.start(); t = null; now what will happen to the created thread?
4. How is garbage collection done in java?
5. How do you write a "ping" routine in java?
6. What are the security restrictions on applets?
Graphics
1. Write a function to check if two rectangles defined as below overlap or not. struct rect { int top, bot, left, right; } r1, r2;
2. Write a SetPixel(x, y) function, given a pointer to the bitmap. Each pixel is represented by 1 bit. There are 640 pixels per row. In each byte, while the bits are numbered right to left, pixels are numbered left to right. Avoid multiplications and divisions to improve performance.
Databases
* 1. You, a designer want to measure disk traffic i.e. get a histogram showing the relative frequency of I/O/second for each disk block. The buffer pool has b buffers and uses LRU replacement policy. The disk block size and buffer pool block sizes are the same. You are given a routine int lru_block_in_position (int i) which returns the block_id of the block in the ith position in the list of blocks managed by LRU. Assume position 0 is the hottest. You can repeatedly call this routine. How would you get the histogram you desire?
Hints and Answers
1. Simply do histogram [lru_block_in_position (b1)] ++ at frequent intervals... The sampling frequency should be close to the disk I/O rate. It can be adjusted by remembering the last block seen in position b. If same, decrease frequency; if different, increase, with exponential decay etc. And of course, take care of overflows in the histogram.
Semaphores
1. Implement a multiplereadersinglewriter lock given a compareandswap instruction. Readers cannot overtake waiting writers.


Computer Architecture
1. Explain what is DMA?
2. What is pipelining?
3. What are superscalar machines and vliw machines?
4. What is cache?
5. What is cache coherency and how is it eliminated?
6. What is write back and write through caches?
7. What are different pipelining hazards and how are they eliminated.
8. What are different stages of a pipe?
9. Explain more about branch prediction in controlling the control hazards
10. Give examples of data hazards with pseudo codes.
11. How do you calculate the number of sets given its way and size in a cache?
12. How is a block found in a cache?
13. Scoreboard analysis.
14. What is miss penalty and give your own ideas to eliminate it.
15. How do you improve the cache performance.
16. Different addressing modes.
17. Computer arithmetic with two's complements.
18. About hardware and software interrupts.
19. What is bus contention and how do you eliminate it.
20. What is aliasing?
21) What is the difference between a latch and a flip flop?
22) What is the race around condition? How can it be overcome?
23) What is the purpose of cache? How is it used?
24) What are the types of memory management?
放飞技术网上面onefi整理的 Microsoft程序员测试题
一．最基本题型（说明：此类题型比较简单）
1.烧一根不均匀的绳，从头烧到尾总共需要1个小时。现在有若干条材质相同的绳子，问如何用烧绳的方法来计时一个小时十五分钟呢？（答案：一根从两头烧 ，并且同是从中间任何一处开始烧。烧完后即为十五分钟。然后再烧一根就是一个小时。）
2.你有一桶果冻，其中有黄色、绿色、红色三种，闭上眼睛抓取同种颜色的两个。抓取多少个就可以确定你肯定有两个同一颜色的果冻？（5秒1分钟）
3.如果你有无穷多的水，一个3公升的提捅，一个5公升的提捅，两只提捅形状上下都不均匀，问你如何才能准确称出4公升的水？（40秒3分钟）
4.一个岔路口分别通向诚实国和说谎国。来了两个人，已知一个是诚实国的，另一个是说谎国的。诚实国永远说实话，说谎国永远说谎话。现在你要去说谎国，但不知道应该走哪条路，需要问这两个人。请问应该怎么问？（20秒2分钟）
5.12个球一个天平，现知道只有一个和其它的重量不同，问怎样称才能用三次就找到那个球。13个呢？（注意此题并未说明那个球的重量是轻是重，所以需要仔细考虑）（5分钟1小时）
6.在9个点上画10条直线，要求每条直线上至少有三个点？（3分钟20分钟）
7.在一天的24小时之中，时钟的时针、分针和秒针完全重合在一起的时候有几次？都分别是什么时间？你怎样算出来的？（5分钟15分钟）
二．没有答案型（说明：这些题显然不是考你智力。而考的是你的反应能力。这种题大多数没有答案，但是要看你的反应喽！）
1.为什么下水道的盖子是圆的？
2.中国有多少辆汽车？
3.将汽车钥匙插入车门，向哪个方向旋转就可以打开车锁？ （按：好在我坐了N次同学的车买菜）
4.如果你要去掉中国的34个省（含自治区、直辖市和港澳特区及台湾省）中的任何一个，你会去掉哪一个，为什么？
5.多少个加油站才能满足中国的所有汽车？
6.想象你站在镜子前，请问，为什么镜子中的影象可以颠倒左右，却不能颠倒上下？
7.为什么在任何旅馆里，你打开热水，热水都会瞬间倾泻而出？
8.你怎样将Excel的用法解释给你的奶奶听？
9.你怎样重新改进和设计一个ATM银行自动取款机？
10.如果你不得不重新学习一种新的计算机语言，你打算怎样着手来开始？
11.如果你的生涯规划中打算在5年内受到奖励，那获取该项奖励的动机是什么？观众是谁？
12.如果微软告诉你，我们打算投资五百万美元来启动你的投资计划，你将开始什么样商业计划？为什么？
13.如果你能够将全世界的电脑厂商集合在一个办公室里，然后告诉他们将被强迫做一件事，那件事将是什么？
三．难题（说明：这类题有一定难度，如果得不到答案，也不能说明什么。如果你想到了解题思路，那么答案马上就能出来。如果想不到思路，那么……就别想解出来了。）
1.你让工人为你工作7天，回报是一根金条，这个金条平分成相连的7段，你必须在每天结束的时候给他们一段金条。如果只允许你两次把金条弄断，你如何给你的工人付费？
2.有一辆火车以每小时15公里的速度离开北京直奔广州，同时另一辆火车每小时20公里的速度从广州开往北京。如果有一只鸟，以30公里每小时的速度和两辆火车同时启动，从北京出发，碰到另一辆车后就向相反的方向返回去飞，就这样依次在两辆火车之间来回地飞，直到两辆火车相遇。请问，这只鸟共飞行了多长的距离？
3.你有四个装药丸的罐子，每个药丸都有一定的重量，被污染的药丸是没被污染的药丸的重量+1。只称量一次，如何判断哪个罐子的药被污染了？
4.门外三个开关分别对应室内三盏灯，线路良好，在门外控制开关时候不能看到室内灯的情况，现在只允许进门一次，确定开关和灯的对应关系？
5.人民币为什么只有1、2、5、10的面值？
6.你有两个罐子以及50个红色弹球和50个蓝色弹球，随机选出一个罐子， 随机选出一个弹球放入罐子，怎么给出红色弹球最大的选中机会？在你的计划里，得到红球的几率是多少？
四．超难题（说明：如果你是第一次看到这种题，并且以前从来没有见过类似的题型，并且能够在半个小时之内做出答案。只能说明你的智力超常……）
第一题 . 五个海盗抢到了100颗宝石，每一颗都一样大小和价值连城。他们决定这么分：
抽签决定自己的号码（1、2、3、4、5）
首先，由1号提出分配方案，然后大家表决，当且仅当超过半数的人同意时，按照他的方案进行分配，否则将被扔进大海喂鲨鱼
如果1号死后，再由2号提出分配方案，然后剩下的4人进行表决，当且仅当超过半数的人同意时，按照他的方案进行分配，否则将被扔入大海喂鲨鱼
依此类推
条件：每个海盗都是很聪明的人，都能很理智地做出判断，从而做出选择。
问题：第一个海盗提出怎样的分配方案才能使自己的收益最大化？
第二题 . 一道关于飞机加油的问题，已知：
每个飞机只有一个油箱，
飞机之间可以相互加油（注意是相互，没有加油机）
一箱油可供一架飞机绕地球飞半圈，
问题：
为使至少一架飞机绕地球一圈回到起飞时的飞机场，至少需要出动几架飞机？（所有飞机从同一机场起飞，而且必须安全返回机场，不允许中途降落，中间没有飞机场）
五．主观题（说明：在以后的工作过程中，我们可定会犯这样那样的错误。既然错误已经酿成，损失在所难免，我们只能想办法把损失减少到最小。如果能巧妙地回答出这些问题，再发生错误的情况下。能让客户有最少的抱怨，公司有最少的损失。）
1.某手机厂家由于设计失误，有可能造成电池寿命比原来设计的寿命短一半（不是冲放电时间），解决方案就是免费更换电池或给50元购买该厂家新手机的折换券。请给所有已购买的用户写信告诉解决方案。
2.一高层领导在参观某博物馆时，向博物馆馆员小王要了一块明代的城砖作为纪念，按国家规定，任何人不得将博物馆收藏品变为私有。博物馆馆长需要如何写信给这位领导，将城砖取回。
3.营业员小姐由于工作失误，将2万元的笔记本电脑以1.2万元错卖给李先生，王小姐的经理怎么写信给李先生试图将钱要回来？
六.算法题（说明：这些题就不是什么花样了，考的是你的基础知识怎么样。再聪明而没有实学的人都将会被这些题所淘汰。）
1.链表和数组的区别在哪里？
2.编写实现链表排序的一种算法。说明为什么你会选择用这样的方法？
3.编写实现数组排序的一种算法。说明为什么你会选择用这样的方法？
4.请编写能直接实现strstr()函数功能的代码。
5.编写反转字符串的程序，要求优化速度、优化空间。
6.在链表里如何发现循环链接？
7.给出洗牌的一个算法，并将洗好的牌存储在一个整形数组里。
8.写一个函数，检查字符是否是整数，如果是，返回其整数值。（或者：怎样只用4行代码编写出一个从字符串到长整形的函数？）
9.给出一个函数来输出一个字符串的所有排列。
10.请编写实现malloc()内存分配函数功能一样的代码。
11.给出一个函数来复制两个字符串A和B。字符串A的后几个字节和字符串B的前几个字节重叠。
12.怎样编写一个程序，把一个有序整数数组放到二叉树中？
13.怎样从顶部开始逐层打印二叉树结点数据？请编程。
14.怎样把一个链表掉个顺序（也就是反序，注意链表的边界条件并考虑空链表）？
2.
Three Microsoft Interview Questions
From http://blog.csdn.net/csumck/archive/2004/11/01/162121.aspx
http://blog.csdn.net/linweixuan/archive/2004/09/28/littlebigendian.aspx
1）实现string toHex(int)把一个十进制转换成十六进制。（完全用算法实现）
第一个题目很简单，就是用十进制数不停的除以16，将所有的余数累加起来便是结果。我用C++简单的实现了一下，下面是代码（VC++.NET/windows xp）：
#include
#include
using namespace std;
string ToHex(int dec)
{
unsigned int udec = (dec>=0)?(dec):(dec), yushu;
int pos = 8;
char Hex[11];
memset(Hex, '0', 9);
Hex[9] = 'H';
Hex[10] = '\0';
do//求余数
{
yushu = udec%16;
Hex[pos] = (yushu>9)?(yushu+55):(yushu+48);
udec = udec/16;
}
while (udec!=0);
if (Hex[pos+1]>64)//如果最高位是字母，则字符串前面补0
Hex[pos] = '0';
else
++pos;
if (dec<0)//如果是负数，在前面加负号
Hex[pos] = '';
return (string(Hex+pos));
2）实现一个计算大位数（如100位以上）相乘结果的函数string multiply(sting,string)。（请完全用算法实现）
第二个题目挺复杂的，大位数的乘法是不能使用atoi将字符串化为整型在相乘的，那样会溢出。模拟手算也不太可能，因为手算的话需要大量的内存记录中间结果。
我想到的比较好的方法是模拟计算机中的乘法。我这个学期刚刚学的计算机组成原理里有讲到关于计算机中原码一位乘法的实现。关于这种方法的具体内容大家可以很容易的在网上找到。使用这种方法计算n位数乘法的话只需2n+2位的缓冲。但是实现起来挺麻烦的，真的行不行我心里也没底。我只是阐述一下我的看法，大家有什么看法欢迎讨论。
那个帖子有牛人给出了C++实现，抄记于下（我都不敢看，太长）：
xiao_wang(小王)
#include "stdafx.h"
#include
#include
using namespace std;
class slong
{
public:
slong()
{
_str = "";
}
slong(string str)
{
string::iterator itor = str.begin();
for(; itor != str.end(); ++itor)
{
if(*itor < '0'  *itor > '9')
throw "the parameter is error.";
}
_str = str;
}
slong(char* s)
{
if(s == NULL)
{
_str = "";
return;
}
size_t size = strlen(s);
for(size_t i = 0; i < size; ++i)
{
if(s[i] < '0'  s[i] > '9')
throw "the parameter is error.";
}
_str = s;
}
slong(const slong& sl)
{
_str = sl._str;
}
slong& operator =(const slong& sl)
{
if(&sl == this)
return *this;
_str = sl._str;
return *this;
}
slong operator *(slong& sl)
{
if(sl._str.length() == 0)
return *this;
int n = static_cast
int m = static_cast
int t = m + n  1; // caculate times
string::reverse_iterator itor1, itor2;
int j = 0;
int k = 0;
int c = 0;
int r = 0;
int v = 0;
char s[2];
string rproduct;
for(int i = 0; i < t; ++i)
{
v = 0;
j = 0;
itor1 = _str.rbegin();
for(; itor1 != _str.rend(); ++itor1)
{
k = 0;
itor2 = sl._str.rbegin();
for(; itor2 != sl._str.rend(); ++itor2)
{
if(j + k == i)
{
v += ctoi(*itor1) * ctoi(*itor2);
break;
}
k++;
}
j++;
if(j > i)
break;
}
v += c;
r = v%10;
c = v/10;
itoa(r, s, 10);
rproduct += s;
}
if(c != 0)
{
itoa(c, s, 10);
rproduct += s;
}
string temp;
temp.resize(product.length());
string::reverse_iterator ritor = product.rbegin();
string::iterator itor = temp.begin();
for(; itor != temp.end(); ++itor)
{
*itor = *ritor;
ritor++;
}
slong product(temp);
return product;
}
int ctoi(char c)
{
return c  48;
}
string value()
{
return _str;
}
private:
string _str;
};
int _tmain(int argc, _TCHAR* argv[])
{
string s1, s2;
cout << "please input first operator" << endl;
cin >> s1;
cout << "please input second operator" << endl;
cin >> s2;
slong sl1(s1);
slong sl2(s2);
slong sl3 = sl1 * sl2;
cout << "the value is :" << endl;
cout << sl3.value() << endl;
char word;
while(cin >> word)
if(word == 'q')
break;
return 0;
}
3) 编写函数判断计算机的字节存储顺序是升序（little endian）还是是降序（bigdian）
1在32位计算机升序排列为
0000 0000 0000 0001 0000 0000 0000 0000
降序为
0000 0000 0000 0000 0000 0000 0000 0001
这个问题应该可以用指针解决。
int i = 1;
char* pc = (char*)(&i);
pc++;
if (*pc > 0) 升序; else 降序;
又看到了一种做法，摘抄于下：
//作者：sutra(只回答经典问题 只提供经典答案)
bool is_little_endian()
{
union {
int i ;
char c ;
} uIc ;
uIc.i = 1 ;
return (uIc.c != 0) ;
}
另一段来自linweixuan得代码
如何判断机器的大小端的问题,在阅读ORBacus的代码中看到的，特此载出
3.1.
int
main ()
{
/* Are we little or big endian? From Harbison&Steele. */
union
{
long l;
char c[sizeof (long)];
} u;
u.l = 1;
exit (u.c[sizeof (long)  1] == 1);
}
3.2.
#include
#include
int
main ()
{
#if BYTE_ORDER != BIG_ENDIAN
not big endian
#endif
;
return 0;
}
3.3.
#include
#include
int
main ()
{
#if !BYTE_ORDER  !BIG_ENDIAN  !LITTLE_ENDIAN
bogus endian macros
#endif
;
return 0;
}
3.
Interview Questions  Microsoft, etc.
From http://halcyon.usc.edu/~kiran/msqs.html
Disclaimer: This page is in no way connected with Microsoft Corporation, its affiliates, friends or haters
What?
Here is a set of questions that I have with me which software guys have asked at interviews in the past, most of them are actually from Microsoft but a few have been pulled together from other places too. I have collected these from friends and would welcome any additions from you. Mail them to kiran AT usc DOT edu. Do send me your solutions, but the intent of this page is to kindle enough interest in you to try similar logic and programming questions.
PLEASE DO NOT REQUEST ME FOR MORE SOLUTIONS!
Why?
I have grown up reading Martin Gardner's Scientific American columns on Mathematical Games and interesting mathematics olympiad problems in high school. I discovered, to my delight, Bentley's Programming Pearls and David Gries' The Science of Programming in my computer science education. There is underlying beauty in mathematics and computer science. Some find it and others hate the subjects. When I found some of the Microsoft interview questions in graduate school, they were similar to mathematical puzzles that I was interested in. I started collecting them more as an illustration of interesting logic puzzles and algorithms in programming, than as an interview aid. If it has morphed into an interview questions page, that is more due to interest from all interviewees out there.
Some of the programming questions have a basic foundation in mathematics and algorithms. If the given data structure has a specific amount of information and the question asks you to extract/modify the given information, it is possible (though not always obvious) to find optimal solutions, and prove that it cannot be done any better, by quantifying the information content. But, there are always elegant and ugly ways to extract the same information. When you manage to find out the optimal solution to a problem, it usually not only turns out to be elegant, but also has the "aha!" factor to it. Try proving on paper the following question from my undergraduate midterm:
1. Everyone Loves All Lovers
2. Romeo Loves Juliet
Therefore, prove (i.e. 1 AND 2 => 3)
3. I Love You
How?
To answer one of the more frequent questions that I get: No! I have never interviewed at Microsoft. In fact, I work in a microprocessor company far removed from any software development (though I work mostly in programming). However, I have had two of my roommates and two more housemates eventually working in Microsoft, in addition to a large number of friends. None of them have contributed to this page AFTER they started working at Microsoft. Microsoft itself does not hold any patents and nor has it invented most of the questions. Most of them come from mathematics and physics books, party puzzles, programming lore and standard textbooks. I know many companies ask similar questions, though Microsoft might have made the practice more common (especially with the manhole cover type of questions).
Usage
I have spent some time in collecting with the intention of their value as a practice session. They are not meant to be exact questions that you need to know and answer in an interview. They are supposed to make you think! Discuss with your friends, colleagues, professors for answers (get your tuition money's worth). I have left the page in simple text format so you can print them out and try them on your flight to the interview in case you are pressed for time. One of the strangest phone calls I remember is from a girl, staying up in a Microsoft provided hotel room in Redmond the night before the interview, asking me about the solution for one of the questions from this page. I hope the rest of you are saner (or do not have my phone number).
Kiran Bondalapati
Ze Meat
Puzzles, Riddles, etc.
Programming Questions
Computer Networks, Databases, etc.
Computer Architecture
Puzzles, Riddles and Others
0. Classic: If a bear walks one mile south, turns left and walks one mile to the east and then turns left again and walks one mile north and arrives at its original position, what is the color of the bear.
ANS. The color of the bear is trivial. The possible solutions to it are interesting. In addition to the trivial north pole, there are additional circles near south pole. Think it out.
* 1. Given a rectangular (cuboidal for the puritans) cake with a rectangular piece removed (any size or orientation), how would you cut the remainder of the cake into two equal halves with one straight cut of a knife?
ANS. Join the centers of the original and the removed rectangle. It works for cuboids too! BTW, I have been getting many questions asking why a horizontal slice across the middle will not do. Please note the "any size or orientation" in the question! Don't get boxed in by the way you cut your birthday cake :) Think out of the box.
2. There are 3 baskets. one of them have apples, one has oranges only and the other has mixture of apples and oranges. The labels on their baskets always lie. (i.e. if the label says oranges, you are sure that it doesn't have oranges only,it could be a mixture) The task is to pick one basket and pick only one fruit from it and then correctly label all the three baskets.
HINT. There are only two combinations of distributions in which ALL the baskets have wrong labels. By picking a fruit from the one labeled MIXTURE, it is possible to tell what the other two baskets have.
3. You have 8 balls. One of them is defective and weighs less than others. You have a balance to measure balls against each other. In 2 weighings how do you find the defective one?
4. Why is a manhole cover round?
HINT. The diagonal of a square hole is larger than the side of a cover!
Alternate answers: 1. Round covers can be transported by one person, because they can be rolled on their edge. 2. A round cover doesn't need to be rotated to fit over a hole.
5. How many cars are there in the USA?
6. You've got someone working for you for seven days and a gold bar to pay them. The gold bar is segmented into seven connected pieces. You must give them a piece of gold at the end of every day. If you are only allowed to make two breaks in the gold bar, how do you pay your worker?
7. One train leaves Los Angeles at 15mph heading for New York. Another train leaves from New York at 20mph heading for Los Angeles on the same track. If a bird, flying at 25mph, leaves from Los Angeles at the same time as the train and flies back and forth between the two trains until they collide, how far will the bird have traveled?
HINT. Think relative speed of the trains.
8. You have two jars, 50 red marbles and 50 blue marbles. A jar will be picked at random, and then a marble will be picked from the jar. Placing all of the marbles in the jars, how can you maximize the chances of a red marble being picked? What are the exact odds of getting a red marble using your scheme?
9. Imagine you are standing in front of a mirror, facing it. Raise your left hand. Raise your right hand. Look at your reflection. When you raise your left hand your reflection raises what appears to be his right hand. But when you tilt your head up, your reflection does too, and does not appear to tilt his/her head down. Why is it that the mirror appears to reverse left and right, but not up and down?
10. You have 5 jars of pills. Each pill weighs 10 gram, except for contaminated pills contained in one jar, where each pill weighs 9 gm. Given a scale, how could you tell which jar had the contaminated pills in just one measurement?
ANS. 1. Mark the jars with numbers 1, 2, 3, 4, and 5.
2. Take 1 pill from jar 1, take 2 pills from jar 2, take 3 pills from jar 3, take 4 pills from jar 4 and take 5 pills from jar 5.
3. Put all of them on the scale at once and take the measurement.
4. Now, subtract the measurement from 150 ( 1*10 + 2*10 + 3*10 + 4*10 + 5*10)
5. The result will give you the jar number which has contaminated pill.
11. If you had an infinite supply of water and a 5 quart and 3 quart pail, how would you measure exactly 4 quarts?
12. You have a bucket of jelly beans. Some are red, some are blue, and some green. With your eyes closed, pick out 2 of a like color. How many do you have to grab to be sure you have 2 of the same?
13. Which way should the key turn in a car door to unlock it?
14. If you could remove any of the 50 states, which state would it be and why?
15. There are four dogs/ants/people at four corners of a square of unit distance. At the same instant all of them start running with unit speed towards the person on their clockwise direction and will always run towards that target. How long does it take for them to meet and where?
HINT. They will meet in the center and the distance covered by them is independent of the path they actually take (a spiral).
16. (from Tara Hovel) A helicopter drops two trains, each on a parachute, onto a straight infinite railway line. There is an undefined distance between the two trains. Each faces the same direction, and upon landing, the parachute attached to each train falls to the ground next to the train and detaches. Each train has a microchip that controls its motion. The chips are identical. There is no way for the trains to know where they are. You need to write the code in the chip to make the trains bump into each other. Each line of code takes a single clock cycle to execute.
You can use the following commands (and only these);
MF  moves the train forward
MB  moves the train backward
IF (P)  conditional that's satisfied if the train is next to a parachute. There is no "then" to this IF statement.
GOTO
ANS.
A: MF
IF (P)
GOTO B
GOTO A

B: MF
GOTO B
Explanation: The first line simply gets them off the parachutes. You need to get the trains off their parachutes so the back train can find the front train's parachute, creating a special condition that will allow it to break out of the code they both have to follow initially. They both loop through A: until the back train finds the front train's parachute, at which point it goes to B: and gets stuck in that loop. The front train still hasn't found a parachute, so it keeps in the A loop. Because each line of code takes a "clock cycle" to execute, it takes longer to execute the A loop than the B loop, therefore the back train (running in the B loop) will catch up to the front train.
Personality
It is best to read some website or a book for questions like these.
1. Tell me the courses you liked and why did you like them.
2. Give an instance in your life in which you were faced with a problem and you tackled it successfully.
3. What is your ideal working environment.
4. Why do you think you are smart.
5. Questions on the projects listed on the Resume.
6. Do you want to know any thing about the company.( Try to ask some relevant and interesting question).
7. How long do you want to stay in USA and why (I guess noncitizens get this)?
8. What is your geographical preference?
9. What are your expectations from the job.

Algorithms and Programming
1. Given a rectangular (cuboidal for the puritans) cake with a rectangular piece removed (any size or orientation), how would you cut the remainder of the cake into two equal halves with one straight cut of a knife ?
2. You're given an array containing both positive and negative integers and required to find the subarray with the largest sum (O(N) a la KBL). Write a routine in C for the above.
3. Given an array of size N in which every number is between 1 and N, determine if there are any duplicates in it. You are allowed to destroy the array if you like. [ I ended up giving about 4 or 5 different solutions for this, each supposedly better than the others ].
4. Write a routine to draw a circle (x ** 2 + y ** 2 = r ** 2) without making use of any floating point computations at all. [ This one had me stuck for quite some time and I first gave a solution that did have floating point computations ].
5. Given only putchar (no sprintf, itoa, etc.) write a routine putlong that prints out an unsigned long in decimal. [ I gave the obvious solution of taking % 10 and / 10, which gives us the decimal value in reverse order. This requires an array since we need to print it out in the correct order. The interviewer wasn't too pleased and asked me to give a solution which didn't need the array ].
6. Give a oneline C expression to test whether a number is a power of 2. [No loops allowed  it's a simple test.]
7. Given an array of characters which form a sentence of words, give an efficient algorithm to reverse the order of the words (not characters) in it.
8. How many points are there on the globe where by walking one mile south, one mile east and one mile north you reach the place where you started.
9. Give a very good method to count the number of ones in a "n" (e.g. 32) bit number.
ANS. Given below are simple solutions, find a solution that does it in log (n) steps.
Iterative
function iterativecount (unsigned int n)
begin
int count=0;
while (n)
begin
count += n & 0x1 ;
n >>= 1;
end
return count;
end
Sparse Count
function sparsecount (unsigned int n)
begin
int count=0;
while (n)
begin
count++;
n &= (n1);
end
return count ;
end
10. What are the different ways to implement a condition where the value of x can be either a 0 or a 1. Apparently the if then else solution has a jump when written out in assembly. if (x == 0) y=a else y=b There is a logical, arithmetic and a data structure solution to the above problem.
11. Reverse a linked list.
12. Insert in a sorted list
13. In a X's and 0's game (i.e. TIC TAC TOE) if you write a program for this give a fast way to generate the moves by the computer. I mean this should be the fastest way possible.
The answer is that you need to store all possible configurations of the board and the move that is associated with that. Then it boils down to just accessing the right element and getting the corresponding move for it. Do some analysis and do some more optimization in storage since otherwise it becomes infeasible to get the required storage in a DOS machine.
14. I was given two lines of assembly code which found the absolute value of a number stored in two's complement form. I had to recognize what the code was doing. Pretty simple if you know some assembly and some fundaes on number representation.
15. Give a fast way to multiply a number by 7.
16. How would go about finding out where to find a book in a library. (You don't know how exactly the books are organized beforehand).
17. Linked list manipulation.
18. Tradeoff between time spent in testing a product and getting into the market first.
19. What to test for given that there isn't enough time to test everything you want to.
20. First some definitions for this problem: a) An ASCII character is one byte long and the most significant bit in the byte is always '0'. b) A Kanji character is two bytes long. The only characteristic of a Kanji character is that in its first byte the most significant bit is '1'.
Now you are given an array of a characters (both ASCII and Kanji) and, an index into the array. The index points to the start of some character. Now you need to write a function to do a backspace (i.e. delete the character before the given index).
21. Delete an element from a doubly linked list.
22. Write a function to find the depth of a binary tree.
23. Given two strings S1 and S2. Delete from S2 all those characters which occur in S1 also and finally create a clean S2 with the relevant characters deleted.
24. Assuming that locks are the only reason due to which deadlocks can occur in a system. What would be a foolproof method of avoiding deadlocks in the system.
25. Reverse a linked list.
Ans: Possible answers 
iterative loop
curr>next = prev;
prev = curr;
curr = next;
next = curr>next
endloop
recursive reverse(ptr)
if (ptr>next == NULL)
return ptr;
temp = reverse(ptr>next);
temp>next = ptr;
return ptr;
end
26. Write a small lexical analyzer  interviewer gave tokens. expressions like "a*b" etc.
27. Besides communication cost, what is the other source of inefficiency in RPC? (answer : context switches, excessive buffer copying). How can you optimize the communication? (ans : communicate through shared memory on same machine, bypassing the kernel _ A Univ. of Wash. thesis)
28. Write a routine that prints out a 2D array in spiral order!
29. How is the readerswriters problem solved?  using semaphores/ada .. etc.
30. Ways of optimizing symbol table storage in compilers.
31. A walkthrough through the symbol table functions, lookup() implementation etc.  The interviewer was on the Microsoft C team.
32. A version of the "There are three persons X Y Z, one of which always lies".. etc..
33. There are 3 ants at 3 corners of a triangle, they randomly start moving towards another corner.. what is the probability that they don't collide.
34. Write an efficient algorithm and C code to shuffle a pack of cards.. this one was a feedback process until we came up with one with no extra storage.
35. The if (x == 0) y = 0 etc..
36. Some more bitwise optimization at assembly level
37. Some general questions on Lex, Yacc etc.
38. Given an array t[100] which contains numbers between 1..99. Return the duplicated value. Try both O(n) and O(nsquare).
39. Given an array of characters. How would you reverse it. ? How would you reverse it without using indexing in the array.
40. Given a sequence of characters. How will you convert the lower case characters to upper case characters. ( Try using bit vector  solutions given in the C lib typec.h)
41. Fundamentals of RPC.
42. Given a linked list which is sorted. How will u insert in sorted way.
43. Given a linked list How will you reverse it.
44. Give a good data structure for having n queues ( n not fixed) in a finite memory segment. You can have some datastructure separate for each queue. Try to use at least 90% of the memory space.
45. Do a breadth first traversal of a tree.
46. Write code for reversing a linked list.
47. Write, efficient code for extracting unique elements from a sorted list of array. e.g. (1, 1, 3, 3, 3, 5, 5, 5, 9, 9, 9, 9) > (1, 3, 5, 9).
48. Given an array of integers, find the contiguous subarray with the largest sum.
ANS. Can be done in O(n) time and O(1) extra space. Scan array from 1 to n. Remember the best subarray seen so far and the best subarray ending in i.
49. Given an array of length N containing integers between 1 and N, determine if it contains any duplicates.
ANS. [Is there an O(n) time solution that uses only O(1) extra space and does not destroy the original array?]
50. Sort an array of size n containing integers between 1 and K, given a temporary scratch integer array of size K.
ANS. Compute cumulative counts of integers in the auxiliary array. Now scan the original array, rotating cycles! [Can someone word this more nicely?]
* 51. An array of size k contains integers between 1 and n. You are given an additional scratch array of size n. Compress the original array by removing duplicates in it. What if k << n?
ANS. Can be done in O(k) time i.e. without initializing the auxiliary array!
52. An array of integers. The sum of the array is known not to overflow an integer. Compute the sum. What if we know that integers are in 2's complement form?
ANS. If numbers are in 2's complement, an ordinary looking loop like for(i=total=0;i< n;total+=array[i++]); will do. No need to check for overflows!
53. An array of characters. Reverse the order of words in it.
ANS. Write a routine to reverse a character array. Now call it for the given array and for each word in it.
* 54. An array of integers of size n. Generate a random permutation of the array, given a function rand_n() that returns an integer between 1 and n, both inclusive, with equal probability. What is the expected time of your algorithm?
ANS. "Expected time" should ring a bell. To compute a random permutation, use the standard algorithm of scanning array from n downto 1, swapping ith element with a uniformly random element <= ith. To compute a uniformly random integer between 1 and k (k < n), call rand_n() repeatedly until it returns a value in the desired range.
55. An array of pointers to (very long) strings. Find pointers to the (lexicographically) smallest and largest strings.
ANS. Scan array in pairs. Remember largestsofar and smallestsofar. Compare the larger of the two strings in the current pair with largestsofar to update it. And the smaller of the current pair with the smallestsofar to update it. For a total of <= 3n/2 strcmp() calls. That's also the lower bound.
56. Write a program to remove duplicates from a sorted array.
ANS. int remove_duplicates(int * p, int size)
{
int current, insert = 1;
for (current=1; current < size; current++)
if (p[current] != p[insert1])
{
p[insert] = p[current];
current++;
insert++;
} else
current++;
return insert;
}
57. C++ ( what is virtual function ? what happens if an error occurs in constructor or destructor. Discussion on error handling, templates, unique features of C++. What is different in C++, ( compare with unix).
58. Given a list of numbers ( fixed list) Now given any other list, how can you efficiently find out if there is any element in the second list that is an element of the first list (fixed list).
59. Given 3 lines of assembly code : find it is doing. IT was to find absolute value.
60. If you are on a boat and you throw out a suitcase, Will the level of water increase.
61. Print an integer using only putchar. Try doing it without using extra storage.
62. Write C code for (a) deleting an element from a linked list (b) traversing a linked list
63. What are various problems unique to distributed databases
64. Declare a void pointer ANS. void *ptr;
65. Make the pointer aligned to a 4 byte boundary in a efficient manner ANS. Assign the pointer to a long number and the number with 11...1100 add 4 to the number
66. What is a far pointer (in DOS)
67. What is a balanced tree
68. Given a linked list with the following property node2 is left child of node1, if node2 < node1 else, it is the right child.
O P


O A


O B


O C
How do you convert the above linked list to the form without disturbing the property. Write C code for that.
O P


O B
/ / / O ? O ?
determine where do A and C go
69. Describe the file system layout in the UNIX OS
ANS. describe boot block, super block, inodes and data layout
70. In UNIX, are the files allocated contiguous blocks of data
ANS. no, they might be fragmented
How is the fragmented data kept track of
ANS. Describe the direct blocks and indirect blocks in UNIX file system
71. Write an efficient C code for 'tr' program. 'tr' has two command line arguments. They both are strings of same length. tr reads an input file, replaces each character in the first string with the corresponding character in the second string. eg. 'tr abc xyz' replaces all 'a's by 'x's, 'b's by 'y's and so on. ANS.
a) have an array of length 26.
put 'x' in array element corr to 'a'
put 'y' in array element corr to 'b'
put 'z' in array element corr to 'c'
put 'd' in array element corr to 'd'
put 'e' in array element corr to 'e'
and so on.
the code
while (!eof)
{
c = getc();
putc(array[c  'a']);
}
72. what is disk interleaving
73. why is disk interleaving adopted
74. given a new disk, how do you determine which interleaving is the best a) give 1000 read operations with each kind of interleaving determine the best interleaving from the statistics
75. draw the graph with performance on one axis and 'n' on another, where 'n' in the 'n' in nway disk interleaving. (a tricky question, should be answered carefully)
76. I was a c++ code and was asked to find out the bug in that. The bug was that he declared an object locally in a function and tried to return the pointer to that object. Since the object is local to the function, it no more exists after returning from the function. The pointer, therefore, is invalid outside.
77. A real life problem  A square picture is cut into 16 squares and they are shuffled. Write a program to rearrange the 16 squares to get the original big square.
78.
int *a;
char *c;
*(a) = 20;
*c = *a;
printf("%c",*c);
what is the output?
79. Write a program to find whether a given m/c is bigendian or littleendian!
80. What is a volatile variable?
81. What is the scope of a static function in C ?
82. What is the difference between "malloc" and "calloc"?
83. struct n { int data; struct n* next}node;
node *c,*t;
c>data = 10;
t>next = null;
*c = *t;
what is the effect of the last statement?
84. If you're familiar with the ? operator x ? y : z
you want to implement that in a function: int cond(int x, int y, int z); using only ~, !, ^, &, +, , <<, >> no if statements, or loops or anything else, just those operators, and the function should correctly return y or z based on the value of x. You may use constants, but only 8 bit constants. You can cast all you want. You're not supposed to use extra variables, but in the end, it won't really matter, using vars just makes things cleaner. You should be able to reduce your solution to a single line in the end though that requires no extra vars.
85. You have an abstract computer, so just forget everything you know about computers, this one only does what I'm about to tell you it does. You can use as many variables as you need, there are no negative numbers, all numbers are integers. You do not know the size of the integers, they could be infinitely large, so you can't count on truncating at any point. There are NO comparisons allowed, no if statements or anything like that. There are only four operations you can do on a variable.
1) You can set a variable to 0.
2) You can set a variable = another variable.
3) You can increment a variable (only by 1), and it's a post increment.
4) You can loop. So, if you were to say loop(v1) and v1 = 10, your loop would execute 10 times, but the value in v1 wouldn't change so the first line in the loop can change value of v1 without changing the number of times you loop.
You need to do 3 things.
1) Write a function that decrements by 1.
2) Write a function that subtracts one variable from another.
3) Write a function that divides one variable by another.
4) See if you can implement all 3 using at most 4 variables. Meaning, you're not making function calls now, you're making macros. And at most you can have 4 variables. The restriction really only applies to divide, the other 2 are easy to do with 4 vars or less. Division on the other hand is dependent on the other 2 functions, so, if subtract requires 3 variables, then divide only has 1 variable left unchanged after a call to subtract. Basically, just make your function calls to decrement and subtract so you pass your vars in by reference, and you can't declare any new variables in a function, what you pass in is all it gets.
Linked lists
* 86. Under what circumstances can one delete an element from a singly linked list in constant time?
ANS. If the list is circular and there are no references to the nodes in the list from anywhere else! Just copy the contents of the next node and delete the next node. If the list is not circular, we can delete any but the last node using this idea. In that case, mark the last node as dummy!
* 87. Given a singly linked list, determine whether it contains a loop or not.
ANS. (a) Start reversing the list. If you reach the head, gotcha! there is a loop!
But this changes the list. So, reverse the list again.
(b) Maintain two pointers, initially pointing to the head. Advance one of them one node at a time. And the other one, two nodes at a time. If the latter overtakes the former at any time, there is a loop!
p1 = p2 = head;
do {
p1 = p1>next;
p2 = p2>next>next;
} while (p1 != p2);
88. Given a singly linked list, print out its contents in reverse order. Can you do it without using any extra space?
ANS. Start reversing the list. Do this again, printing the contents.
89. Given a binary tree with nodes, print out the values in preorder/inorder/postorder without using any extra space.
90. Reverse a singly linked list recursively. The function prototype is node * reverse (node *) ;
ANS.
node * reverse (node * n)
{
node * m ;
if (! (n && n > next))
return n ;
m = reverse (n > next) ;
n > next > next = n ;
n > next = NULL ;
return m ;
}
91. Given a singly linked list, find the middle of the list.
HINT. Use the single and double pointer jumping. Maintain two pointers, initially pointing to the head. Advance one of them one node at a time. And the other one, two nodes at a time. When the double reaches the end, the single is in the middle. This is not asymptotically faster but seems to take less steps than going through the list twice.
Bitmanipulation
92. Reverse the bits of an unsigned integer.
ANS.
#define reverse(x) (x=x>>16(0x0000ffff&x)<<16, x=(0xff00ff00&x)>>8(0x00ff00ff&x)<<8, x=(0xf0f0f0f0&x)>>4(0x0f0f0f0f&x)<<4, x=(0xcccccccc&x)>>2(0x33333333&x)<<2, x=(0xaaaaaaaa&x)>>1(0x55555555&x)<<1)
* 93. Compute the number of ones in an unsigned integer.
ANS.
#define count_ones(x) (x=(0xaaaaaaaa&x)>>1+(0x55555555&x), x=(0xcccccccc&x)>>2+(0x33333333&x), x=(0xf0f0f0f0&x)>>4+(0x0f0f0f0f&x), x=(0xff00ff00&x)>>8+(0x00ff00ff&x), x=x>>16+(0x0000ffff&x))
94. Compute the discrete log of an unsigned integer.
ANS.
#define discrete_log(h) (h=(h>>1)(h>>2), h=(h>>2), h=(h>>4), h=(h>>8), h=(h>>16), h=(0xaaaaaaaa&h)>>1+(0x55555555&h), h=(0xcccccccc&h)>>2+(0x33333333&h), h=(0xf0f0f0f0&h)>>4+(0x0f0f0f0f&h), h=(0xff00ff00&h)>>8+(0x00ff00ff&h), h=(h>>16)+(0x0000ffff&h))
If I understand it right, log2(2) =1, log2(3)=1, log2(4)=2..... But this macro does not work out log2(0) which does not exist! How do you think it should be handled?
* 95. How do we test most simply if an unsigned integer is a power of two?
ANS. #define power_of_two(x) \ ((x)&&(~(x&(x1))))
96. Set the highest significant bit of an unsigned integer to zero.
ANS. (from Denis Zabavchik) Set the highest significant bit of an unsigned integer to zero
#define zero_most_significant(h) \
(h&=(h>>1)(h>>2), \
h=(h>>2), \
h=(h>>4), \
h=(h>>8), \
h=(h>>16))
97. Let f(k) = y where k is the yth number in the increasing sequence of nonnegative integers with the same number of ones in its binary representation as y, e.g. f(0) = 1, f(1) = 1, f(2) = 2, f(3) = 1, f(4) = 3, f(5) = 2, f(6) = 3 and so on. Given k >= 0, compute f(k).
Others
98. A character set has 1 and 2 byte characters. One byte characters have 0 as the first bit. You just keep accumulating the characters in a buffer. Suppose at some point the user types a backspace, how can you remove the character efficiently. (Note: You cant store the last character typed because the user can type in arbitrarily many backspaces)
99. What is the simples way to check if the sum of two unsigned integers has resulted in an overflow.
100. How do you represent an nary tree? Write a program to print the nodes of such a tree in breadth first order.
101. Write the 'tr' program of UNIX. Invoked as
tr str1 str2. It reads stdin and prints it out to stdout, replacing every occurance of str1[i] with str2[i].
e.g. tr abc xyz
to be and not to be < input
to ye xnd not to ye < output

Networks and Security
1. How do you use RSA for both authentication and secrecy?
2. What is ARP and how does it work?
3. What's the difference between a switch and a router?
4. Name some routing protocols? (RIP,OSPF etc..)
5. How do you do authentication with message digest(MD5)? (Usually MD is used for finding tampering of data)
6. How do you implement a packet filter that distinguishes following cases and selects first case and rejects second case.
i) A host inside the corporate n/w makes a ftp request to outside host and the outside host sends reply.
ii) A host outside the network sends a ftp request to host inside. for the packet filter in both cases the source and destination fields will look the same.
7. How does traceroute work? Now how does traceroute make sure that the packet follows the same path that a previous (with ttl  1) probe packet went in?
8. Explain Kerberos Protocol ?
9. What are digital signatures and smart cards?
10. Difference between discretionary access control and mandatory access control?
Java
1. How do you find the size of a java object (not the primitive type) ?
ANS. type cast it to string and find its s.length()
2. Why is multiple inheritance not provided in Java?
3. Thread t = new Thread(); t.start(); t = null; now what will happen to the created thread?
4. How is garbage collection done in java?
5. How do you write a "ping" routine in java?
6. What are the security restrictions on applets?
Graphics
1. Write a function to check if two rectangles defined as below overlap or not. struct rect { int top, bot, left, right; } r1, r2;
2. Write a SetPixel(x, y) function, given a pointer to the bitmap. Each pixel is represented by 1 bit. There are 640 pixels per row. In each byte, while the bits are numbered right to left, pixels are numbered left to right. Avoid multiplications and divisions to improve performance.
Databases
* 1. You, a designer want to measure disk traffic i.e. get a histogram showing the relative frequency of I/O/second for each disk block. The buffer pool has b buffers and uses LRU replacement policy. The disk block size and buffer pool block sizes are the same. You are given a routine int lru_block_in_position (int i) which returns the block_id of the block in the ith position in the list of blocks managed by LRU. Assume position 0 is the hottest. You can repeatedly call this routine. How would you get the histogram you desire?
Hints and Answers
1. Simply do histogram [lru_block_in_position (b1)] ++ at frequent intervals... The sampling frequency should be close to the disk I/O rate. It can be adjusted by remembering the last block seen in position b. If same, decrease frequency; if different, increase, with exponential decay etc. And of course, take care of overflows in the histogram.
Semaphores
1. Implement a multiplereadersinglewriter lock given a compareandswap instruction. Readers cannot overtake waiting writers.


Computer Architecture
1. Explain what is DMA?
2. What is pipelining?
3. What are superscalar machines and vliw machines?
4. What is cache?
5. What is cache coherency and how is it eliminated?
6. What is write back and write through caches?
7. What are different pipelining hazards and how are they eliminated.
8. What are different stages of a pipe?
9. Explain more about branch prediction in controlling the control hazards
10. Give examples of data hazards with pseudo codes.
11. How do you calculate the number of sets given its way and size in a cache?
12. How is a block found in a cache?
13. Scoreboard analysis.
14. What is miss penalty and give your own ideas to eliminate it.
15. How do you improve the cache performance.
16. Different addressing modes.
17. Computer arithmetic with two's complements.
18. About hardware and software interrupts.
19. What is bus contention and how do you eliminate it.
20. What is aliasing?
21) What is the difference between a latch and a flip flop?
22) What is the race around condition? How can it be overcome?
23) What is the purpose of cache? How is it used?
24) What are the types of memory management?