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
        # a+b+c+b=2*(a+b)
        # a+b+(b+c)n=2(a+b)
        slow = pHead
        fast = pHead
        while fast != None and fast.next != None:
            fast = fast.next.next
            slow = slow.next
            if fast == slow:
                while pHead != slow:
                    pHead = pHead.next
                    slow = slow.next
                return slow
        return None