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
        if not pHead or not pHead.next:
            return None
        slow, fast = pHead, pHead
        while fast and fast.next:
            slow = slow.next
            fast = fast.next.next
            if slow == fast:
                break
        if slow != fast:
            return None
        fast = pHead
        while slow!=fast:
            slow = slow.next
            fast = fast.next
        return slow