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
        fast = slow = pHead
        while fast != None and fast.next != None:
            slow = slow.next
            fast = fast.next.next
            if fast == slow:
                break

        if fast == None or fast.next == None:
            return None
        
        fast = pHead
        while fast != slow:
            fast = fast.next
            slow = slow.next
        return fast