【LeetCode】141. 循环链表

题目

给定一个链表，判断链表中是否有环。

思路

也可以用哈希表，不过空间复杂度会是O(n)。

代码

# 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 is None or head.next is None:
            return False
        slow = head
        fast = head.next
        while slow != fast:
            if fast.next is None or fast.next.next is None:
                return False
            slow = slow.next
            fast = fast.next.next
        return True