141. Linked List Cycle

Tags:

• Easy
• linked list
• recommend

Link

use slow and fast (pointer)indicator

# 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 slow:

            slow = slow.next

            if fast:
                fast = fast.next
            if fast:
                fast = fast.next

            if slow == fast:
                break

        return slow != None