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# Find loop in a linked list

  • Loop in a linked list refers to an endless cycle in the list such that if we start traversing the list we will never reach the end of the linked list (i.e. NULL).

  • We take two pointers slow and fast and point them to the first node by equating to head.

  • We move the fast pointer by two nodes and slow pointer by one node at a time.

  • If the link part of the fast pointer or the fast pointer becomes NULL, it means there is no loop and we have reached the end of the list.

  • Otherwise, If slow and fast pointers meet at some point i.e. they both point to the same element, it means that there is a loop in the linked list.

# Source Code - C++

int findLoop (Node *head)
{
Node *slow, *fast;
slow=head;
fast=head;
 while (fast!=NULL && fast->link!=NULL )
 {
 fast= fast->link->link;
 slow = slow->link;
  if (slow ==  fast)
  {
  return 1;   //loop found
  }
 }
return 0;      //No loop, reached end of list