141.linked-list-cycle.py

#
# @lc app=leetcode id=141 lang=python3
#
# [141] Linked List Cycle
#

# @lc code=start
# 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:
        arrived = set()
        while head:
            if head.next in arrived:
                return True
            else:
                arrived.add(head)
            head = head.next
        return False
    def hasCycle2(self, head: Optional[ListNode]) -> bool:
        try:
            slow = head
            fast = head.next
            while slow is not fast:
                slow = slow.next
                fast = fast.next.next
            return True
        except:
            return False
# @lc code=end