题解 | 链表中环的入口结点

import java.util.*;
/*
 public class ListNode {
    int val;
    ListNode next = null;

    ListNode(int val) {
        this.val = val;
    }
}
*/
public class Solution {

    public ListNode EntryNodeOfLoop(ListNode pHead) {
        if(pHead == null)
            return null;
        ListNode fast=pHead,slow=pHead;
        boolean meet = false;
        while(fast != null&&fast.next != null){            
            fast = fast.next.next;            
            slow = slow.next;
            if(fast == slow){
                meet = true;
                break;
            }
        }
        if(!meet) return null;
        fast = pHead;
        while(fast != slow){
            fast = fast.next;
            slow = slow.next;
        }
        return fast;
    }
}