题解 | #判断链表中是否有环#

/**
 * 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==nullptr) return false;
        ListNode* fast=head;
        ListNode* slow=head;
        while(fast->next&&fast->next->next){
            fast=fast->next->next;
            slow=slow->next;
            if(fast==slow) return true;
        }
        return false;
    }
};

判断链表中是否有环：双指针法，一快一慢，若有环，他们会在环中相遇