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
        ans = None
        if pHead==None or pHead.next==None:
            return ans
        fast = pHead
        slow = pHead
        while fast and slow:
            if fast.next:
                fast = fast.next.next
                slow = slow.next
                if fast == slow:
                    fast = pHead
                    while not (fast==slow):
                        fast = fast.next
                        slow = slow.next
                    return slow
            else:
                return ans
        return ans