【2024考研】题解5 | #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) {
       //write code here
       //1.特例表空
       if(head == NULL)
            return false;
        
       //2.定义快慢两个指针
       ListNode *fast = head;
       ListNode *slow = head;
        //没有环的情况下快指针肯定先到到表尾
       while(fast != NULL && fast->next != NULL){
            fast = fast->next->next;
            slow = slow->next;
            //快慢指针相遇即肯定有环
            if(slow == fast)
                return true;
       }
       return false;
    }
};