Detect Cycle in Linked List

Problem Statement

You’re given the pointer to the head node of a linked list. Find whether the list contains any cycle (or loop). A linked list is said to contain cycle if any node is re-visited while traversing the list. The head pointer given may be null meaning that the list is empty.

Input Format 
You have to complete the int HasCycle(Node* head) method which takes one argument - the head of the linked list. You should NOT read any input from stdin/console. Number of nodes in a linked list doesn't exceed 100.

Output Format 
Check whether the linked list has a cycle and return 1 if there is a cycle. Otherwise, return 0. Do NOT print anything to stdout/console.

Sample Input

1 --> NULL

1 --> 2 --> 3
      ^     |
      |     |
       -----                           

Sample Output

0
1

Explanation 
1. First list has no cycle, hence return 0 
2. Second list is shown to have a cycle, hence return 1.

Note 
After first solving the problem by yourself, see Floyd's cycle-finding algorithm for an efficient solution which uses O(N) time and O(1) additional memory.

/*
  Detect loop in a linked list 
  List could be empty also
  Node is defined as 
  struct Node
  {
     int data;
     struct Node *next;
  }
*/
int HasCycle(Node* head)
{
   // Complete this function
   // Do not write the main method
    if(head == NULL || head->next == NULL || head->next->next == NULL){
        return 0;
    }
    Node* slow = head;
    Node* fast = head->next->next;
    while(fast->next->next != NULL && slow->next != NULL){
        if(fast == slow){
            return 1;
        }else{
            fast = fast->next->next;
            slow = slow->next;
        }
    }
    return 0;
}