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
# 用集合判断是否重复访问，若重复访问该节点，则其为循环入口
class Solution:
    def EntryNodeOfLoop(self, pHead):
        # write code here
        this = pHead
        visit = {pHead}
        while this:
            this = this.next
            if this in visit:
                return this
            visit.add(this)
        return None