链表环中的入口点 编程之美 leecode 学习

http://www.cnblogs.com/hiddenfox/p/3408931.html 说的很细

 

/**

 * Definition for singly-linked list.

 * class ListNode {

 *     int val;

 *     ListNode next;

 *     ListNode(int x) {

 *         val = x;

 *         next = null;

 *     }

 * }

 */

public class Solution {

    

             

             

        

        

        

    public static ListNode detectCycle(ListNode head) {

    ListNode slow = head;

    ListNode fast = head;



    while (true) {

        if (fast == null || fast.next == null) {

            return null;    

        }

        slow = slow.next;

        fast = fast.next.next;

        if (fast == slow) {

            break;   

        }

    }



    slow = head;    

    while (slow != fast) {    

        slow = slow.next;

        fast = fast.next;

    }

    return slow;

}

}l