Detect Cycle - Hacker Rank Solution

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.
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 /*
  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
    Node* fast = head, *slow = head; 
   while(fast!= NULL){ 
     fast = fast->next->next; 
     slow = slow->next; 
     if(fast == slow){ 
       return 1; 
     } 
   }return 0;
}
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