题解 | #链表中环的入口结点#

# -*- coding:utf-8 -*-
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None
class Solution:
    def EntryNodeOfLoop(self, pHead):
        # write code here
        p1=pHead
        p2=pHead
        m="null"
        while p2 is  not None and p2.next is not None:
            p1=p1.next
            p2=p2.next.next
            if p1==p2:
                p1=pHead
                if p1==p2:
                    return p1
                while p2 is  not None and p2.next is not None:
                    p1=p1.next
                    p2=p2.next
                    if p1==p2:
                        return p1
                return m