Description

Linked List Two Pointers

Python

快慢指针法（注意不要出现None.next的情况）

# 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 not head or not head.next:
            return False
        slow, fast = head, head.next
        while slow != fast:
            if not fast or not fast.next:
                return False
            slow, fast = slow.next, fast.next.next
        return True

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