刷题记录第二十七天-环形链表II

class Solution {
public:
    ListNode *detectCycle(ListNode *head) {
        ListNode* slow=head;
        ListNode* fast=head;
        while(fast!=NULL&&fast->next!=NULL){
            slow=slow->next;
            fast=fast->next->next;
            if(slow==fast)break;
        }
        if(fast==NULL||fast->next==NULL)return NULL;
        slow = head;
        while(slow!=fast){
            slow=slow->next;
            fast=fast->next;
        }
        return slow;
    }
};