【牛客题霸每日一题】NC4 判断链表中是否有环 题解
若链表中有环，则设置两个指针均从头结点开始行进，快指针一次走两步，慢指针一次走一步，若有环，则快慢指针总会相遇，返回true，否则返回 false
代码如下：
/**
* 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 == NULL) return false;
ListNode *fast = head;
ListNode *slow = head;
while(fast->next != NULL && fast->next->next != NULL) {
fast = fast->next->next;
slow = slow->next;
if(fast == slow) return true;
}
return false;
}
}; 