141_linked_list_cycle.py

#!/usr/bin/env python
# -*- coding: UTF-8 -*-

##########################################################################
#	> File Name: 141_linked_list_cycle.py
#	> Author: Tingjian Lau
#	> Mail: tjliu@mail.ustc.edu.cn
#	> Created Time: 2016/05/16
#########################################################################

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

class Solution(object):
    # Floyd判圈算法
    def hasCycle(self, head):
        """
        :type head: ListNode
        :rtype: bool
        """
        slow, fast = head, head
        
        while fast and fast.next:
            slow, fast = slow.next, fast.next.next
            if slow is fast:
                return True
        
        return False