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++;
} 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 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.
* 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.
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).
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
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?
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?
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.
* 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.
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?