Friday, July 25, 2008

Technical Interview Questions on Computer Science

The following is a list of questions which have been floating around some
Internet circles. They are excellent prep questions for a technical interview.

I haven't made any attempt to clean them up, spelling or organization wise.

Don't bother asking me for the answers,
1) I don't have an answer key.
2) It'd do you good to think.

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 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 32 bit number.
(caution: looping through testing each bit is not a solution).

10. What are the different ways to say, 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 =x

There is a logical, arithmetic and a datastructure soln to the above

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 gast way to generate the moves by the computer. I mean this
should be the fasteset 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

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.

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 optimise 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 interv. was on the Microsoft C team.

32. A version of the "There are three persons X Y Z, one of which always lies"..


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 algo 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
- sol given in the C lib -> typec.h)

41. Fundas of RPC.

42. Given a linked list which is sorted. How will u insert in sorted

43. Given a linked list How will you reverse it.

44. Tell me the courses you liked and why did you like them.

45. Give an instance in your life in which u were faced with a
problem and you tackled it successfully.

46. What is your ideal working environment. ( They usually
to hear that u can work in group also.)

47. Why do u think u are smart.

48. Questions on the projects listed on the Resume.

49. Do you want to know any thing about the company.( Try to ask some
relevant and interesting question).

50. How long do u want to stay in USA and why?

51. What are your geographical preference?

52. What are your expecctations from the job.

53. 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.

54. Do a breadth first traversal of a tree.

55. Write code for reversing a linked list.

56. 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).

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

62. write C code for
deleting an element from a linked listy
traversing a linked list
efficient way of elimiating duplicates from an array

63. what are various problems unique to distributed databases

64. declare a void pointer
a) void *ptr;

65. make the pointer aligned to a 4 byte boundary in a efficient manner
a) 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
els, it is the right child.


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

/ \
/ \
/ \
O ? O ?

determine where do A and C go

69. Describe the file system layout in the UNIX OS
a) describe boot block, super block, inodes and data layout

70. In UNIX, are the files allocated contiguous blocks of data
a) no, they might be fragmented
how is the fragmented data kept track of
a) 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.
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 performace 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 sqaures and
they are shuffled. Write a program to rearrange the 16 squares to
get the original big square.