linkedlist2.cpp

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode *detectCycle(ListNode *head) {
        ListNode* slow =head;
        ListNode *fast =head;
        while(fast && fast->next)
        {
            slow =slow->next;
            fast=fast->next->next;
            if(slow==fast) break;
        }
       
        if(!(fast && fast->next)) return NULL;
        while(head!=slow)
        {
            head=head->next;
            slow=slow->next;
            
        }
        return head;    }
};