package main

type ListNode struct {
	Val  int
	Next *ListNode
}

// This solution uses O(1) memory, but
// runtime duration is a bit more
// unpredictable with a maximum complexity
// of O(n^2) I think.
/**
 * Definition for singly-linked list.
 * type ListNode struct {
 *     Val int
 *     Next *ListNode
 * }
 */
func hasCycle(head *ListNode) bool {
	slow, fast := head, head
	for fast != nil && fast.Next != nil {
		slow, fast = slow.Next, fast.Next.Next
		if slow == fast {
			return true
		}
	}
	return false
}