package top100liked

import (
	"fmt"
	"testing"
)

// https://leetcode.cn/problems/linked-list-cycle/description/?envType=study-plan-v2&envId=top-100-liked

type ListNode struct {
	Val  int
	Next *ListNode
}

// func hasCycle(head *ListNode) bool {
// 	_map := make(map[*ListNode]bool)
// 	for head != nil {
// 		if _map[head] {
// 			return true
// 		}
// 		_map[head] = true
// 		head = head.Next
// 	}
// 	return false
// }

func hasCycle(head *ListNode) bool {
	if head == nil || head.Next == nil {
		return false
	}
	slow, fast := head, head.Next
	for fast != slow {
		if fast == nil || fast.Next == nil {
			return false
		}
		slow = slow.Next
		fast = fast.Next.Next
	}
	return true
}

func TestS24(t *testing.T) {
	input := &ListNode{
		Val: 3,
		Next: &ListNode{
			Val: 2,
			Next: &ListNode{
				Val: 0,
				Next: &ListNode{
					Val:  -4,
					Next: nil,
				},
			},
		},
	}
	input.Next.Next.Next.Next = input.Next
	fmt.Println(hasCycle(input))
}