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 = pHead
        slow = pHead

        while True:
            if fast.next and fast.next.next:
                fast = fast.next.next
            else:
                return None
            slow = slow.next
            if fast == slow:
                break
        
        fast = pHead # 这里用 slow = pHead 也行
        while fast != slow:
            fast = fast.next
            slow = slow.next
        return slow

                

神奇的题目，第21行用fast或者slow都行