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LinkedListCycle.java

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/*

Author: King, higuige@gmail.com

Date: Oct 5, 2014

Problem: Linked List Cycle

Difficulty: Easy

Source: http://oj.leetcode.com/problems/linked-list-cycle/

Notes:

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

Follow up:

Can you solve it without using extra space?

Solution: two pointers.

*/

/**

* Definition for singly-linked list.

* class ListNode {

* int val;

* ListNode next;

* ListNode(int x) {

* val = x;

* next = null;

* }

* }

*/

public class Solution {

public boolean 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) break;

}

if (fast == null || fast.next == null) return false;

return true;

}

}