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Linked List Cycle

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Descripition

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

Solution

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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 == NULL || head->next == NULL) return false;
        ListNode* before = head;
        ListNode* after = head;
        while (after != NULL) {
            before = before->next;
            after = after->next;
            if (after == NULL) return false;
            after = after->next;
            if (before == after) return true;
        }
        return false;
    }
};

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​ 5 - 6

4步

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​ 4 5

4步

1 2

3

3步

1 2

两部