## Friday, December 16, 2011

There were 4 rounds for selection procedure. First round was a written test, second round was group interview and 3rd and 4th rounds were technical interview. Each round had eliminations. Total 143 students were eligible for written test and 16 students were selected for the next round, ie. group interview. Only 8 students were able to go for 3rd round of technical interview. In 3rd round 4 more students were eliminated and remaining 4 students went for final round of technical interview. Only 1 student got an offer finally from Microsoft.

Following is the detail about each round.

Note: All examples which I will give here are just for your understanding. Interviewer was not giving any examples. Hardly 2 – 3 time interviewer gave examples.

Round 1: Written test

Paper style: 3 subjective questions

Time limit: 1½ hour

Question 1: Finding output....

It was string cruncher program. First remove all repeated consecutive substring with length 1, then delete substring of length 2 and so on...

Example : string is “abcabeccced”

After removing repeated substring of length 1: “abcababceccced” --> “abcababceced” (2 ,c, are removed)

After removing repeated substring of length 2: “abcababceced” --> “abcabceced” (substring “ab” is removed)

and so on...

Question 2: Writing a program.

Definition: You are given 3 integer arrays A, B and C of length n1, n2 and n3 respectively. All arrays are sorted. We define triplet of these 3 arrays as (x,y,z) where x is any integer from A, y from B and z from C. We define distance of triplet as maximum difference among triplet elements, i.e. Maximum of x – y, y – z or z – x. Write a program to find minimum triplet distance. (means there are n1*n2*n3 number of possible triplets are possible...among all triplets which triplet has minimum distance...Give only distance, but not triplet elements). Your program must be as much efficient as possible.

Question 3: Writing program.

Definition: You are given 2 integer numbers in linked list form. Add those 2 numbers.

Example: First number is 234 and second number is 35. So, you are provided with 2 linked lists 2->3->4 and 3->5. Your answer must be 2->6->9. (Make sure to take care of carry number). This example was given in paper.

Round 2: Group Interview

All candidates who had cleared the written test were called for group interview. Here we were given 3 problems one by one. Time limit was between 15 to 20 minutes. Once they gave problem definition we were supposed to think on it and discuss our ideas and logic about solving that problem with one of the representatives from Microsoft. Once that representative was convinced with our logic then we had to write code for that problem on paper.

Problem 1: You are given a string. Develop a function to remove duplicate characters from that string. String could be of any length. Your algorithm must be in space. If you wish you can use constant size extra space which is not dependent any how on string size. Your algorithm must be of complexity of O(n). Example: Given string is BANANAS. Output must be BANS. All repeated characters are removed.

Problem 2: You have a tree and address of its root. Write an efficient program to test whether a given tree is Binary search Tree or not. (Hint: In-order traversal of binary search tree is sorted in increasing order. Use this property to develop program)

Problem 3: You have 2 sorted lists and a function that merge that 2 lists such that output is again sorted and duplicates are removed. That means output is union of those 2 lists in sorted form.

Example: First list is 2->3->5->6->8 and second list is 4->5->6->7 and output of function is 2->3->4->5->6->7->8.

Develop test cases to test given function such that your test cases ensures that given function works for every situation. That is if inputs are valid then it gives proper output in any case or otherwise it shows error message.

Round 3: First Technical Interview

All those who had cleared group interview were called for first technical interview. They were taking minimum 2 hours for first interview. Some of us also faced interview for 3 or more hours.

Round 4: Second Technical Interview

All those who had cleared first technical interview were called for second interview. This was last round of interview. They took 1½ to 2 hours for this second interview.

I don,t remember all the questions which were asked to me in both interviews. But still some of the questions which I can remember (almost 80 to 90% questions) are listed below.

In both interview they ask questions from C/C++, java, OS, Data structure and algorithms, Microprocessors and compiler constructions. With this, they also asked me to develop more than 6 to 8 programs. You can develop all programs in 5 to 7 minutes. But after writing program they asked to find its complexity and try to reduce the complexity and write the program again. In this way it took almost 15 to 20 min for each program. Some took less than 15 minutes also.

Some of the interview questions are as follows:

1. You are given a linked list and block size k. Reverse block of size k from list.

For example you are given linked list of 1000 nodes and block size is 5 then instead of reversing whole list, reverse first 5 elements, then 6 to 10 elements, then 11 to 15 elements, and so on...You have singly linked list and your algorithm which you will implement must be in space, that is no extra space is allowed.

2. You are given a tree and any 2 nodes of that tree. Find common parent of both nodes. Develop as much efficient program as you can.

3. In unix there is a command called “tail”. Implement that command in C.

4. Some questions about race condition (OS)

5. Questions related to semaphores.

6. Questions related to mutex. Applications of mutex. How to implement mutex in OS?

7. Questions about Critical region (OS).

8. How to ensure that race condition doesn,t occur. Give your view as you are OS designer.

9. How to ensure that each process lock the critical region before they enter in it. As OS designer How will you force the process to do this?

10. Questions on IPC

11. Questions on Shared memory and Message passing mechanism.

12. Difference between system call and API call

13. How system call works? What happens when system call is invoked?

14. Different types of system calls?

15. Some questions from microprocessor. About Interrupts

16. Types of Interrupts. What happened when interrupt is called?

17. You are given a hard copy of a program which contains some errors. Your job is to find all types of errors from it. And discuss why is it an error. Write correct program for the same.

18. You are given a linked list and a number n. You also have a function to delete all nodes from that list which are at position which multiple of n in the list.

Example: if number is 3 then delete 3rd, 6th, 9th ,...nodes form the list. Develop a program that tests whether given function works properly or not. (In short they are asking me to develop general program for all test cases. By running that program all tests can be performed.)

19. Questions on java. Exception handling

20. Need of catch and finally block in java exception handling..

21. How will you create your own exception.. Explain with example.

22. Some questions on compiler construction. What is parser? What is input to the parser and what is output of parser? Difference between top down and bottom up parser.

23. F(1) = 1.

F(2n) = F (n) and F(2n+1) = F(n) + F(n+1).

Develop recursive program.

24. You are given a string which contains some special characters. You also have set of special characters. You are given other string (call it as pattern string). Your job is to write a program to replace each special characters in given string by pattern string. You are not allowed to create new resulting string. You need to allocate some new memory to given existing string but constraint is you can only allocate memory one time. Allocate memory exactly what you need not more not less.

25. Assume that your friend is writing a book . He gives you a file that contains that book. Your job is to develop an algorithm for indexing of that book. In every book there is one index at end which contains some words which are not there in normal vocabulary dictionary. It also contains page number for reference. You can use any data structure you want. You need to justify why you have used that data structure and also need to justify your logic.

26. Question from my B.E. final semester project. Asked me to explain whole project.

27. Question from everything written on my resume.

28. Question from my every project I did. They asked me to explain each project and then how to do some modification? That modification will be suggested by interviewer himself.

29. My experience in Teaching assistantship.

30. They had my written test answer sheet. They opened it and asked me to explain why I gave that output or why I implement that logic. How did I arrive to that solution which I had written in answer sheet.

31. In written test, for second question I had implement a program which was not much efficient. During interview they ask me to optimize my program. They also gave hint to optimize it.

32. During group interview, in second problem I was only able to discuss logic I was unable to develop program in given time limit. Interviewer knew this. She asked me to develop that program during interview.

33. Which is your favorite software tool? If you are allowed to add any feature in it which feature you will add?

34. Which is your favorite subject? Some questions from that subject.

35. Something about yourself , your hobbies, interests, strengths and weakness.

MICROSOFT PAPER ON 26th JULY

Selection procedure and interview questions of Microsoft at Dhirubhai Ambani Institute of Information and Communication Technology (DA-IICT)

There were 4 rounds for selection procedure. First round was a written test, second round was group interview and 3rd and 4th rounds were technical interview. Each round had eliminations. Total 143 students were eligible for written test and 16 students were selected for the next round, ie. group interview. Only 8 students were able to go for 3rd round of technical interview. In 3rd round 4 more students were eliminated and remaining 4 students went for final round of technical interview. Only 1 student got an offer finally from Microsoft.

Following is the detail about each round.

Note: All examples which I will give here are just for your understanding. Interviewer was not giving any examples. Hardly 2 – 3 time interviewer gave examples.

Round 1: Written test

Paper style: 3 subjective questions

Time limit: 1½ hour

Question 1: Finding output....

It was string cruncher program. First remove all repeated consecutive substring with length 1, then delete substring of length 2 and so on...

Example : string is “abcabeccced”

After removing repeated substring of length 1: “abcababceccced” --> “abcababceced” (2 ,c, are removed)

After removing repeated substring of length 2: “abcababceced” --> “abcabceced” (substring “ab” is removed)

and so on...

Question 2: Writing a program.

Definition: You are given 3 integer arrays A, B and C of length n1, n2 and n3 respectively. All arrays are sorted. We define triplet of these 3 arrays as (x,y,z) where x is any integer from A, y from B and z from C. We define distance of triplet as maximum difference among triplet elements, i.e. Maximum of x – y, y – z or z – x. Write a program to find minimum triplet distance. (means there are n1*n2*n3 number of possible triplets are possible...among all triplets which triplet has minimum distance...Give only distance, but not triplet elements). Your program must be as much efficient as possible.

Question 3: Writing program.

Definition: You are given 2 integer numbers in linked list form. Add those 2 numbers.

Example: First number is 234 and second number is 35. So, you are provided with 2 linked lists 2->3->4 and 3->5. Your answer must be 2->6->9. (Make sure to take care of carry number). This example was given in paper.

Round 2: Group Interview

All candidates who had cleared the written test were called for group interview. Here we were given 3 problems one by one. Time limit was between 15 to 20 minutes. Once they gave problem definition we were supposed to think on it and discuss our ideas and logic about solving that problem with one of the representatives from Microsoft. Once that representative was convinced with our logic then we had to write code for that problem on paper.

Problem 1: You are given a string. Develop a function to remove duplicate characters from that string. String could be of any length. Your algorithm must be in space. If you wish you can use constant size extra space which is not dependent any how on string size. Your algorithm must be of complexity of O(n). Example: Given string is BANANAS. Output must be BANS. All repeated characters are removed.

Problem 2: You have a tree and address of its root. Write an efficient program to test whether a given tree is Binary search Tree or not. (Hint: In-order traversal of binary search tree is sorted in increasing order. Use this property to develop program)

Problem 3: You have 2 sorted lists and a function that merge that 2 lists such that output is again sorted and duplicates are removed. That means output is union of those 2 lists in sorted form.

Example: First list is 2->3->5->6->8 and second list is 4->5->6->7 and output of function is 2->3->4->5->6->7->8.

Develop test cases to test given function such that your test cases ensures that given function works for every situation. That is if inputs are valid then it gives proper output in any case or otherwise it shows error message.

Round 3: First Technical Interview

All those who had cleared group interview were called for first technical interview. They were taking minimum 2 hours for first interview. Some of us also faced interview for 3 or more hours.

Round 4: Second Technical Interview

All those who had cleared first technical interview were called for second interview. This was last round of interview. They took 1½ to 2 hours for this second interview.

I don,t remember all the questions which were asked to me in both interviews. But still some of the questions which I can remember (almost 80 to 90% questions) are listed below.

In both interview they ask questions from C/C++, java, OS, Data structure and algorithms, Microprocessors and compiler constructions. With this, they also asked me to develop more than 6 to 8 programs. You can develop all programs in 5 to 7 minutes. But after writing program they asked to find its complexity and try to reduce the complexity and write the program again. In this way it took almost 15 to 20 min for each program. Some took less than 15 minutes also.

Some of the interview questions are as follows:

1. You are given a linked list and block size k. Reverse block of size k from list.

For example you are given linked list of 1000 nodes and block size is 5 then instead of reversing whole list, reverse first 5 elements, then 6 to 10 elements, then 11 to 15 elements, and so on...You have singly linked list and your algorithm which you will implement must be in space, that is no extra space is allowed.

2. You are given a tree and any 2 nodes of that tree. Find common parent of both nodes. Develop as much efficient program as you can.

3. In unix there is a command called “tail”. Implement that command in C.

4. Some questions about race condition (OS)

5. Questions related to semaphores.

6. Questions related to mutex. Applications of mutex. How to implement mutex in OS?

7. Questions about Critical region (OS).

8. How to ensure that race condition doesn,t occur. Give your view as you are OS designer.

9. How to ensure that each process lock the critical region before they enter in it. As OS designer How will you force the process to do this?

10. Questions on IPC

11. Questions on Shared memory and Message passing mechanism.

12. Difference between system call and API call

13. How system call works? What happens when system call is invoked?

14. Different types of system calls?

15. Some questions from microprocessor. About Interrupts

16. Types of Interrupts. What happened when interrupt is called?

17. You are given a hard copy of a program which contains some errors. Your job is to find all types of errors from it. And discuss why is it an error. Write correct program for the same.

18. You are given a linked list and a number n. You also have a function to delete all nodes from that list which are at position which multiple of n in the list.

Example: if number is 3 then delete 3rd, 6th, 9th ,...nodes form the list. Develop a program that tests whether given function works properly or not. (In short they are asking me to develop general program for all test cases. By running that program all tests can be performed.)

19. Questions on java. Exception handling

20. Need of catch and finally block in java exception handling..

21. How will you create your own exception.. Explain with example.

22. Some questions on compiler construction. What is parser? What is input to the parser and what is output of parser? Difference between top down and bottom up parser.

23. F(1) = 1.

F(2n) = F (n) and F(2n+1) = F(n) + F(n+1).

Develop recursive program.

24. You are given a string which contains some special characters. You also have set of special characters. You are given other string (call it as pattern string). Your job is to write a program to replace each special characters in given string by pattern string. You are not allowed to create new resulting string. You need to allocate some new memory to given existing string but constraint is you can only allocate memory one time. Allocate memory exactly what you need not more not less.

25. Assume that your friend is writing a book . He gives you a file that contains that book. Your job is to develop an algorithm for indexing of that book. In every book there is one index at end which contains some words which are not there in normal vocabulary dictionary. It also contains page number for reference. You can use any data structure you want. You need to justify why you have used that data structure and also need to justify your logic.

26. Question from my B.E. final semester project. Asked me to explain whole project.

27. Question from everything written on my resume.

28. Question from my every project I did. They asked me to explain each project and then how to do some modification? That modification will be suggested by interviewer himself.

29. My experience in Teaching assistantship.

30. They had my written test answer sheet. They opened it and asked me to explain why I gave that output or why I implement that logic. How did I arrive to that solution which I had written in answer sheet.

31. In written test, for second question I had implement a program which was not much efficient. During interview they ask me to optimize my program. They also gave hint to optimize it.

32. During group interview, in second problem I was only able to discuss logic I was unable to develop program in given time limit. Interviewer knew this. She asked me to develop that program during interview.

33. Which is your favorite software tool? If you are allowed to add any feature in it which feature you will add?

34. Which is your favorite subject? Some questions from that subject.

35. Something about yourself , your hobbies, interests, strengths and weakness.

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 i-th 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 (b-1)] ++ 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 multiple-reader-single-writer lock given a compare-and-swap 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?

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 sub-array 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 one-line 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 &= (n-1);

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 2-D array in spiral order!

29. How is the readers-writers problem solved? - using semaphores/ada .. etc.

30. Ways of optimizing symbol table storage in compilers.

31. A walk-through 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(n-square).

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 data-structure 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 sub-array 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 sub-array seen so far and the best sub-array 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 i-th element with a uniformly random element <= i-th. 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 largest-so-far and smallest-so-far. Compare the larger of the two strings in the current pair with largest-so-far to update it. And the smaller of the current pair with the smallest-so-far 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[insert-1]){p[insert] = p[current];current++;insert++;} elsecurrent++;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 list63. What are various problems unique to distributed databases64. 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 number66. What is a far pointer (in DOS)67. What is a balanced tree68. 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 CHow 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 go69. Describe the file system layout in the UNIX OSANS. describe boot block, super block, inodes and data layout70. In UNIX, are the files allocated contiguous blocks of dataANS. no, they might be fragmentedHow is the fragmented data kept track ofANS. Describe the direct blocks and indirect blocks in UNIX file system71. 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 codewhile (!eof){c = getc();putc(array[c - ,a,]);}72. what is disk interleaving73. why is disk interleaving adopted74. 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 statistics75. draw the graph with performance on one axis and ,n, on another, where ,n, in the ,n, in n-way 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 big-endian or little-endian!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 pre-order/in-order/post-order 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.

Bit-manipulation

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&(x-1))))

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 y-th number in the increasing sequence of non-negative 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 n-ary 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

MICROSOFT PAPER AND PATTERN

The following are actual questions from actual interviews conducted by

Microsoft employees on the main campus. Microsoft Consultants are

sometimes allowed to have a life, so questions asked of them during

interviews don,t really count and aren,t listed.

The questions tend to follow some basic themes:

Riddles

Algorithms

Applications

Thinkers

Riddles

Why is a manhole cover round?

How many cars are there in the USA? (A popular variant is "How many gas

stations are there in the USA?")

How many manhole covers are there in the USA?

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?

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?

Imagine a disk spinning like a record player turn table. Half of the

disk is black and the other is white. Assume you have an unlimited

number

of color sensors. How many sensors would you have to place around the

disk to determine the direction the disk is spinning? Where would they

be placed?

Imagine an analog clock set to 12 o,clock. Note that the hour and

minute hands overlap. How many times each day do both the hour and

minute

hands overlap? How would you determine the exact times of the day that

this occurs?

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?

Pairs of primes separated by a single number are called prime pairs.

Examples are 17 and 19. Prove that the number between a prime pair is

always divisible by 6 (assuming both numbers in the pair are greater

than

6). Now prove that there are no ,prime triples.,

There is a room with a door (closed) and three light bulbs. Outside the

room there are three switches, connected to the bulbs. You may

manipulate the switches as you wish, but once you open the door you

can,t

change them. Identify each switch with its bulb.

Suppose you had 8 billiard balls, and one of them was slightly heavier,

but the only way to tell was by putting it on a scale against another.

What,s the fewest number of times you,d have to use the scale to find

the heavier ball?

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?

You have 4 jars of pills. Each pill is a certain weight, except for

contaminated pills contained in one jar, where each pill is weight + 1.

How could you tell which jar had the contaminated pills in just one

measurement?

The SF Chronicle has a word game where all the letters are scrambled up

and you have to figure out what the word is. Imagine that a scrambled

word is 5 characters long:

How many possible solutions are there?

What if we know which 5 letters are being used?

Develop an algorithm to solve the word.

There are 4 women who want to cross a bridge. They all begin on the

same side. You have 17 minutes to get all of them across to the other

side. It is night. There is one flashlight. A maximum of two people can

cross at one time. Any party who crosses, either 1 or 2 people, must

have

the flashlight with them. The flashlight must be walked back and forth,

it cannot be thrown, etc. Each woman walks at a different speed. A pair

must walk together at the rate of the slower woman,s pace.

Woman 1: 1 minute to cross

Woman 2: 2 minutes to cross

Woman 3: 5 minutes to cross

Woman 4: 10 minutes to cross

For example if Woman 1 and Woman 4 walk across first, 10 minutes have

elapsed when they get to the other side of the bridge. If Woman 4 then

returns with the flashlight, a total of 20 minutes have passed and you

have failed the mission. What is the order required to get all women

across in 17 minutes? Now, what,s the other way?

If you had an infinite supply of water and a 5 quart and 3 quart pail,

how would you measure exactly 4 quarts?

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?

If you have two buckets, one with red paint and the other with blue

paint, and you take one cup from the blue bucket and poor it into the

red

bucket. Then you take one cup from the red bucket and poor it into the

blue bucket. Which bucket has the highest ratio between red and blue?

Prove it mathematically.

Algorithms

What,s the difference between a linked list and an array?

Implement a linked list. Why did you pick the method you did?

Implement an algorithm to sort a linked list. Why did you pick the

method you did? Now do it in O(n) time.

Describe advantages and disadvantages of the various stock sorting

algorithms.

Implement an algorithm to reverse a linked list. Now do it without

recursion.

Implement an algorithm to insert a node into a circular linked list

without traversing it.

Implement an algorithm to sort an array. Why did you pick the method

you did?

Implement an algorithm to do wild card string matching.

Implement strstr() (or some other string library function).

Reverse a string. Optimize for speed. Optimize for space.

Reverse the words in a sentence, i.e. "My name is Chris" becomes "Chris

is name My." Optimize for speed. Optimize for space.

Find a substring. Optimize for speed. Optimize for space.

Compare two strings using O(n) time with constant space.

Suppose you have an array of 1001 integers. The integers are in random

order, but you know each of the integers is between 1 and 1000

(inclusive). In addition, each number appears only once in the array,

except

for one number, which occurs twice. Assume that you can access each

element of the array only once. Describe an algorithm to find the

repeated

number. If you used auxiliary storage in your algorithm, can you find

an

algorithm that does not require it?

Count the number of set bits in a number. Now optimize for speed. Now

optimize for size.

Multiple by 8 without using multiplication or addition. Now do the same

with 7.

Add numbers in base n (not any of the popular ones like 10, 16, 8 or 2

-- I hear that Charles Simonyi, the inventor of Hungarian Notation,

favors -2 when asking this question).

Write routines to read and write a bounded buffer.

Write routines to manage a heap using an existing array.

Implement an algorithm to take an array and return one with only unique

elements in it.

Implement an algorithm that takes two strings as input, and returns the

intersection of the two, with each letter represented at most once. Now

speed it up. Now test it.

Implement an algorithm to print out all files below a given root node.

Given that you are receiving samples from an instrument at a constant

rate, and you have constant storage space, how would you design a

storage algorithm that would allow me to get a representative readout

of

data, no matter when I looked at it? In other words, representative of

the

behavior of the system to date.

How would you find a cycle in a linked list?

Give me an algorithm to shuffle a deck of cards, given that the cards

are stored in an array of ints.

The following asm block performs a common math function, what is it?

cwd xor ax, dx

sub ax, dx

Imagine this scenario:

I/O completion ports are communictaions ports which take handles to

files, sockets, or any other I/O. When a Read or Write is submitted to

them, they cache the data (if necessary), and attempt to take the

request

to completion. Upon error or completion, they call a user-supplied

function to let the users application know that that particular request

has

completed. They work asynchronously, and can process an unlimited

number of simultaneous requests.

Design the implementation and thread models for I/O completion ports.

Remember to take into account multi-processor machines.

Write a function that takes in a string parameter and checks to see

whether or not it is an integer, and if it is then return the integer

value.

Write a function to print all of the permutations of a string.

Implement malloc.

Write a function to print the Fibonacci numbers.

Write a function to copy two strings, A and B. The last few bytes of

string A overlap the first few bytes of string B.

How would you write qsort?

How would you print out the data in a binary tree, level by level,

starting at the top?

Applications

How can computer technology be integrated in an elevator system for a

hundred story office building? How do you optimize for availability?

How

would variation of traffic over a typical work week or floor or time of

day affect this?

How would you implement copy-protection on a control which can be

embedded in a document and duplicated readily via the Internet?

Define a user interface for indenting selected text in a Word document.

Consider selections ranging from a single sentence up through

selections of several pages. Consider selections not currently visible

or only

partially visible. What are the states of the new UI controls? How will

the user know what the controls are for and when to use them?

How would you redesign an ATM?

Suppose we wanted to run a microwave oven from the computer. What kind

of software would you write to do this?

What is the difference between an Ethernet Address and an IP address?

How would you design a coffee-machine for an automobile.

If you could add any feature to Microsoft Word, what would it be?

How would you go about building a keyboard for 1-handed users?

How would you build an alarm clock for deaf people?

Thinkers

How are M&Ms made?

If you had a clock with lots of moving mechanical parts, you took it

apart piece by piece without keeping track of the method of how it was

disassembled, then you put it back together and discovered that 3

important parts were not included; how would you go about reassembling

the

clock?

If you had to learn a new computer language, how would you go about

doing it?

You have been assigned to design Bill Gates bathroom. Naturally, cost

is not a consideration. You may not speak to Bill.

What was the hardest question asked of you so far today?

If MS told you we were willing to invest $5 million in a start up of

your choice, what business would you start? Why?

If you could gather all of the computer manufacturers in the world

together into one room and then tell them one thing that they would be

compelled to do, what would it be?

Explain a scenario for testing a salt shaker.

If you are going to receive an award in 5 years, what is it for and who

is the audience?

How would you explain how to use Microsoft Excel to your grandma?

Why is it that when you turn on the hot water in any hotel, for

example, the hot water comes pouring out almost instantaneously?

Why do you want to work at Microsoft?

Suppose you go home, enter your house/apartment, hit the light switch,

and nothing happens - no light floods the room. What exactly, in order,

are the steps you would take in determining what the problem was?

Interviewer hands you a black pen and says nothing but "This pen is

red."

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