最近的題目都偏簡單 ><

題目說明

找到 linked list 有沒有環

解法

使用快慢指針，如果兩個指針走著走著相遇了，代表必定有環

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

class Solution:
    def hasCycle(self, head: Optional[ListNode]) -> bool:
        slow, fast = head, head
        while fast and fast.next:
            slow = slow.next
            fast = fast.next.next
            if slow == fast:
                return True
        return False