package top100liked

import (
	"fmt"
	"testing"
)

// https://leetcode.cn/problems/swap-nodes-in-pairs/description/?envType=study-plan-v2&envId=top-100-liked

type ListNode struct {
	Val  int
	Next *ListNode
}

func swapPairs(head *ListNode) *ListNode {
	if head == nil {
		return nil
	}
	if head.Next == nil {
		return head
	}
	dummy := &ListNode{0, head}
	p1, p2, p3 := dummy, dummy.Next, dummy.Next.Next
	for {
		p1.Next = p3
		p2.Next = p3.Next
		p3.Next = p2
		p2, p3 = p3, p2
		for range 2 {
			if p3.Next == nil {
				return dummy.Next
			}
			p1 = p1.Next
			p2 = p2.Next
			p3 = p3.Next
		}
	}
}

// func swapPairs(head *ListNode) *ListNode {
//     dummyHead := &ListNode{0, head}
//     temp := dummyHead
//     for temp.Next != nil && temp.Next.Next != nil {
//         node1 := temp.Next
//         node2 := temp.Next.Next
//         temp.Next = node2
//         node1.Next = node2.Next
//         node2.Next = node1
//         temp = node1
//     }
//     return dummyHead.Next
// }

func Test(t *testing.T) {
	input1 := &ListNode{
		Val: 1,
		Next: &ListNode{
			Val: 2,
			Next: &ListNode{
				Val: 3,
				Next: &ListNode{
					Val:  4,
					Next: nil,
				},
			},
		},
	}
	input2 := &ListNode{
		Val: 1,
		Next: &ListNode{
			Val: 2,
			Next: &ListNode{
				Val:  3,
				Next: nil,
			},
		},
	}
	output := swapPairs(input1)
	for output != nil {
		fmt.Print(output.Val, " ")
		output = output.Next
	}
	fmt.Println()
	output = swapPairs(input2)
	for output != nil {
		fmt.Print(output.Val, " ")
		output = output.Next
	}
}