141.py

#==================================================
#==>      Title: linked-list-cycle
#==>     Author: Zhang zhen                   
#==>      Email: hustmatnoble.gmail.com
#==>     GitHub: https://github.com/MatNoble
#==>       Date: 1/14/2021
#==================================================

"""
https://leetcode-cn.com/problems/linked-list-cycle/
"""

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

class Solution:
    def hasCycle(self, head: ListNode) -> bool:
        if head == None:
            return False
        slow, fast = head, head
        while fast != None and fast.next != None:
            slow = slow.next
            fast = fast.next.next
            if slow == fast:
                return True
        return False