Linked List Cycle II

题目思路

判断给定链表中是否存在环，如果存在环返回环的起点。

参考这篇文章。

题目代码:

/*** 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 == nullptr || head->next == nullptr) return nullptr;ListNode *fast = head;ListNode *slow = head;while(fast->next && fast->next->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 nullptr;}
};