C Interview Questions and Answers


Linked Lists -- Can you tell me how to check whether a linked list is circular?

Create two pointers, and set both to the start of the list. Update each as follows:

while (pointer1) {

pointer1 = pointer1->next;

pointer2 = pointer2->next;

if (pointer2) pointer2=pointer2->next;

if (pointer1 == pointer2) {

print ("circularn");



If a list is circular, at some point pointer2 will wrap around and be either at
the item just before pointer1, or the item before that. Either way, its either 1
or 2 jumps until they meet.

Posted by:Richards