package top100liked

import (
	"fmt"
	"testing"
)

// https://leetcode.cn/problems/remove-nth-node-from-end-of-list/description/?envType=study-plan-v2&envId=top-100-liked

type ListNode struct {
	Val  int
	Next *ListNode
}

// func removeNthFromEnd(head *ListNode, n int) *ListNode {
// 	pre := &ListNode{Next: head}
// 	p := head
// 	l := 0
// 	for p != nil {
// 		l++
// 		p = p.Next
// 	}
// 	p1 := pre
// 	p2 := pre.Next.Next
// 	for range l - n {
// 		p1 = p1.Next
// 		p2 = p2.Next
// 	}
// 	p1.Next = p2
// 	return pre.Next
// }

// 双指针
func removeNthFromEnd(head *ListNode, n int) *ListNode {
	dummy := &ListNode{0, head}
	first, second := head, dummy
	for range n {
		first = first.Next
	}
	for first != nil {
		first = first.Next
		second = second.Next
	}
	second.Next = second.Next.Next
	return dummy.Next
}

func Test(t *testing.T) {
	input1 := &ListNode{
		Val: 1,
		Next: &ListNode{
			Val: 2,
			Next: &ListNode{
				Val: 3,
				Next: &ListNode{
					Val: 4,
					Next: &ListNode{
						Val:  5,
						Next: nil,
					},
				},
			},
		},
	}
	input2 := &ListNode{
		Val: 1,
		Next: &ListNode{
			Val:  2,
			Next: nil,
		},
	}
	output := removeNthFromEnd(input1, 2)
	for output != nil {
		fmt.Print(output.Val, " ")
		output = output.Next
	}
	fmt.Println()
	output = removeNthFromEnd(input2, 1)
	for output != nil {
		fmt.Print(output.Val, " ")
		output = output.Next
	}
}