package main

type ListNode struct {
	Val  int
	Next *ListNode
}

func main() {

}

func hasCycle(head *ListNode) bool {
	hash := make(map[*ListNode]struct{})
	for head != nil {
		if _, ok := hash[head.Next]; ok {
			return true
		}
		hash[head] = struct{}{}
		head = head.Next
	}

	return false
}