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142.cpp
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30 lines (30 loc) · 715 Bytes
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/**
* 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) {
if(head==NULL || head->next==NULL) return NULL;
ListNode *fast,*slow;
fast=head;
slow=head;
while(fast && fast->next){
slow=slow->next;
fast=fast->next->next;
if(slow==fast){
fast=head;
while(fast!=slow){
fast=fast->next;
slow=slow->next;
}
return fast;
}
}
return NULL;
}
};