Some of the Technical Interview Questions For Computer Science Programmers ….
The following is a list of questions which have been floating around some
Internet circles. They are excellent prep questions for a technical interview.
Don’t bother asking me for the answers,
1) I don’t have an answer key.
2) It’d do you good to think and have discussion using comments.
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=0
else
y =x
There is a logical, arithmetic and a datastructure soln 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 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 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.
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”.. 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 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 way.
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 storage.
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 (answer: void *ptr;)
65. make the pointer aligned to a 4 byte boundary in a efficient manner
(answer: 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.
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
(answer: describe boot block, super block, inodes and data layout)
70. In UNIX, are the files allocated contiguous blocks of data
(answer: 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.
(answer: 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
(answer: 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.