LeetCode 142

Linked List Cycle II

Given a linked list, return the node where the cycle begins.
If there is no cycle, return null.

Note: Do not modify the linked list.

Follow up:
Can you solve it without using extra space?

 /*************************************************************************
     > File Name: LeetCode142.c
     > Author: Juntaran
     > Mail: JuntaranMail@gmail.com
     > Created Time: Mon 16 May 2016 19:46:12 PM CST
  ************************************************************************/

 /*************************************************************************

     Linked List Cycle II

     Given a linked list, return the node where the cycle begins.
     If there is no cycle, return null.

     Note: Do not modify the linked list.

     Follow up:
     Can you solve it without using extra space?

  ************************************************************************/

 #include <stdio.h>

 /**
  * Definition for singly-linked list.
  * struct ListNode {
  *     int val;
  *     struct ListNode *next;
  * };
  */
 struct ListNode *detectCycle(struct ListNode *head)
 {

     struct ListNode *fast = head;
     struct ListNode *slow = head;

     int count1 = ;
     int count2 = ;
     while( slow && fast && fast->next )
     {
         fast = fast->next->next;
         slow = slow->next;

         if( slow == fast )
         {
             slow = head;
             while( slow != fast )
             {
                 slow = slow->next;
                 fast = fast->next;
             }
             return slow;
         }
     }
     return NULL;
 }