141. Linked List Cycle

Total Accepted: 158161
Total Submissions: 443008
Difficulty: Easy
Contributors: Admin

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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来源： https://leetcode.com/problems/linked-list-cycle/

分析

见LintCode Cycle I 和 II

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

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