leetCode-linkedListCycle判断链表是否有环

题目

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

Follow up:

Can you solve it without using extra space?

分析

判断链表是否有环,采用快慢指针,如果相遇则表示有环

AC代码

/**
* Definition for singly-linked list.
* struct ListNode {
*     int val;
*     ListNode *next;
*     ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
bool hasCycle(ListNode *head) {
if(!head || !head->next){
return false;
}
ListNode* slow = head;
ListNode* fast = head->next;
while(fast->next && fast->next->next && fast != slow){
fast = fast->next->next;
slow = slow->next;
}
return fast == slow;
}
};