C Puzzles

yet another place for C puzzles

Sunday, May 30, 2010


Big int implementation

a question from Microsoft.

Implement BigInt class (with +,-,*,-,^)

answers link:

Sunday, May 23, 2010


subarray with largest sum

find the sum of contiguous subarray within a one-dimensional array of numbers which has the largest sum

answer :

Wednesday, May 19, 2010


How do you reverse the words in a string?

How do you reverse the words in a string?

"My name is Yet Another Software Junk"
"Junk Software Another Yet is name My"

1. first reverse the string
"My name is Yet Another Software Junk" to
"knuJ erawtfoS rehtonA teY si eman yM"

2. reverse word by word now
"knuJ erawtfoS rehtonA teY si eman yM" to
"Junk Software Another Yet is name My"


delete a node from circular singlely linked list with O(1)

You are given a circular single linked list of sufficiently many number of
nodes(say more than 1 crore). You need to delete a node say P and you are
given a pointer to P in the circular single list.

Suggest the most efficient methodology of deleting the node P from the
circular single linked list without rounding about the circular single
linked list.


We have a list looking like: ... -> Node(i-1) -> Node(i) -> Node(i+1) -> ... and we need to delete Node(i).

  1. Copy data (not pointer, the data itself) from Node(i+1) to Node(i), the list will look like: ... -> Node(i-1) -> Node(i+1) -> Node(i+1) -> ...
  2. delete the second Node(i+1), it doesn't require pointer to the previous node.

Friday, March 19, 2010


Finding the Nth-node-from-the-end of a linked list.

answer in my mind:

1. travel the linked list for n times
(if you hit null in between, return null)
2. Then travel the linked list till end
(remember to increment the n-node pointer along with traversal)


one linked list meet another linked list

Linked List B meet Linked List A at node J. find J

linked list A. heada->x->....->J->......->z->null
linked list B headb->y->....->J


sorted array right shfted

A sorted array . for eg: 2,3,6,8,11,23,56,89
It is right shifted unknown times eg: 23,56,89,2,3,6,8,11
now search an element in the array... say eg:56.
(no linear search allowed.)

answer in my mind:
1. first find the largest element by log(n)
2. now remove the first part or last part depends on search element.
3. now log(n) search for the item.

Monday, March 15, 2010


queues with two stacks

implement queue with two stacks

answer link


Big Endian or Little Endian

a c-program to find the endians of a processor?


unsigned int i = 0xabcdefgh;

unsigned char *pc = (unsigned char *) &i;

if (*pc == 0xgh) {
/* little endian */
} else {
/* big endian */

Thursday, June 28, 2007


compiler hack

Here is a C puzzle I(PCE) got from Bestin:

You have a magical program `a.c'. When you type `cc a.c', your compiler appears to hang (ie, you don't get back the prompt). Now,during this time, you will be able to type any program `b.c' in the standard input and type Ctrl-D. Once you do this, you get back the prompt. Now, you type `a.out' and magic, what you get will be the output of program `b.c'! Question is, what is this program `a.c'?

Monday, February 19, 2007


curly bracket matching

Not a puzzle exactly.

Q. Are you familiar with curly bracket matching in vi editor?
(FYI: you may use % to find matching curly brackets)

implement this feature in 'your own' editor.

[you may even give a single-WORD-answer :-]

To simplify the question...
imagine a text with curly brackets like the following

2nd curly matches with 3rd
1st curly with last one
4th with 9th

Now start writing the program.


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