142. 环形链表 II - 力扣（LeetCode）

代码

# encoding = utf-8
# 开发者：Alen
# 开发时间： 20:16
# "Stay hungry，stay foolish."

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution(object):
    def detectCycle(self, head):
        seen = set()
        node = head
        while node:
            if node in seen:
                return node
            seen.add(node)
            node = node.next
        return None

结果

解题步骤：https://www.bilibili.com/video/BV1SdXxBsEWM/?vd_source=15b4bc8968fa5203cc470cb68ff72c96