# -*- 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