package q141

type ListNode struct {
	Val  int
	Next *ListNode
}

func hasCycle(head *ListNode) bool {
	if head == nil {
		return false
	}

	p1, p2 := head, head
	for {
		for range 2 {
			p2 = p2.Next
			switch p2 {
			case nil:
				return false
			case p1:
				return true
			}
		}
		p1 = p1.Next
	}
}

var _ = hasCycle