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linkedListCycle.II.cpp
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linkedListCycle.II.cpp
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// Source : https://oj.leetcode.com/problems/linked-list-cycle-ii/
// Author : Hao Chen
// Date : 2014-07-03
/**********************************************************************************
*
* Given a linked list, return the node where the cycle begins. If there is no cycle, return null.
*
* Follow up:
* Can you solve it without using extra space?
*
*
**********************************************************************************/
/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
private:
ListNode *p1, *p2;
public:
bool hasCycle(ListNode *head) {
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;
}
ListNode *detectCycle(ListNode *head) {
if (hasCycle(head)==false){
return NULL;
}
p1 = head;
while (p1!=p2) {
p1 = p1->next;
p2 = p2->next;
}
return p1;
}
};