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141. linked list cycle

难度:Easy

刷题内容

原题连接

  • https://leetcode.com/problems/linked-list-cycle/
  • 内容描述

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

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

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˼· **- ʱ�临�Ӷ�: O(N)*- �ռ临�Ӷ�: O(1)***

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/**
 * 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* l1 = head,*l2 = head ->next;
        while(true)
        {
            if(l2 == nullptr || l2 ->next == nullptr)
                return false;
            if(l1 == l2)
                return true;
            l1 = l1 ->next;
            l2 = l2 ->next ->next;
        }
    }
};


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