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141. Linked List Cycle

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

Follow up:
Can you solve it without using extra space?

一个+1 一个+2 看看能不能相遇。注意代码不要写乱了...以后尽量用p1  p2 这种变量名,不要用p ,q让人看着眼花缭乱

/** * 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) {        ListNode * p1 = head;        ListNode * p2 = head;        while (p2 != nullptr && p2->next!=nullptr) {            p1 = p1->next;            p2 = p2->next->next;            if (p1 == p2) {                return true;            }        }        return false;    }};

 

141. Linked List Cycle