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// Source : https://oj.leetcode.com/problems/linked-list-cycle/

// Author : Hao Chen

// Date : 2014-07-03

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

* Given a linked list, determine if it has a cycle in it.

* Follow up:

* Can you solve it without using extra space?

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

bool hasCycle(ListNode *head) {

ListNode* p1;

ListNode* p2;

if (head==NULL) return false;

p1=head;

p2=head;

while (p1!=NULL && p2!=NULL){

p1=p1->next;

if (p2->next == NULL) return false;

p2=p2->next->next;

if (p1==p2) return true;

}

return false;

}