【leetcode刷题笔记】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?

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题解：参见http://www.cnblogs.com/sunshineatnoon/p/3825032.html

代码如下：

/**
 * 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) {
        ListNode p1 = head;
        ListNode p2 = head;
        
        while(p2 != null){
            p1 = p1.next;
            p2 = p2.next;
            if(p2 != null)
                p2 = p2.next;
            else 
                return false;
            if(p1 == p2)
                return true;
        }
        return false;
    }
}