判断链表中是否有环

问题简述

判断给定的链表中是否有环。

判断链表中是否有环_牛客题霸_牛客网

思路：快慢指针

Python

# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

#
# @param head ListNode类 
# @return bool布尔型
#
class Solution:
    def hasCycle(self , head: ListNode) -> bool:
        
        fast = slow = head
        has_cycle = False
        while fast and fast.next:
            slow = slow.next
            fast = fast.next.next
            if slow == fast:
                has_cycle = True
                break
        
        return has_cycle