题解 | 判断链表中是否有环 | python双指针
判断链表中是否有环
http://www.nowcoder.com/practice/650474f313294468a4ded3ce0f7898b9
判断是否有环，需要两个指针，一个一次走一步，一个一次走两步，相遇说明链表有环，快指针到头结束循环代表没有换
# 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 ):
# write code here
if not head:
return False
slow , fast = head , head
while fast and fast.next:
# 慢指针走一步，快指针走两步
slow = slow.next
fast = fast.next.next
# 相遇说明有环，返回True
if slow == fast:
return True
return False
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