题解 | #链表中环的入口结点#

双指针法：
当判断出有环，让快指针指向链表头，然后和慢指针每次均前进一个节点，相遇的节点即入口。

import java.util.*;

public class Solution {

    public ListNode EntryNodeOfLoop(ListNode pHead) {
        ListNode fast = pHead;
        ListNode slow = pHead;
        while(fast != null && fast.next != null){
            fast = fast.next.next;
            slow = slow.next;

            if(fast == slow){
                fast = pHead;

                while(fast != slow){
                    fast = fast.next;
                    slow = slow.next;
                }

                return fast;
            }
        }

        return null;
    }
}