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
        d={}  #记录入度
        p=pHead
        while p:
            if p not in d:
                d[p]=1
            else:
                return p  #if 有环则有两个入度，遍历链表，首先有两个入度则为入口
            p=p.next
        return None