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
        s1 = set()

        while pHead:
            s1.add(pHead)
            pHead=pHead.next
            if pHead in s1:
                return pHead
        return None