题解 | #信封嵌套#

package main

import (
	"bufio"
	"fmt"
	"os"
	"sort"
	"strconv"
	"strings"
)

/*
*
二维数组排序
*/
func solution(envelopes [][]int) int {
	if len(envelopes) == 0 {
		return 0
	}
	//排序：第一个元素升序、第二元素降序
	sort.Slice(envelopes, func(i, j int) bool {
		a, b := envelopes[i], envelopes[j]
		return a[0] < b[0] || (a[0] == b[0] && a[1] > b[1])
	})

	//计算最长递增子列：只看第二个元素的递增（严格递增）
	dp := make([]int, len(envelopes))
	for i := range dp {
		dp[i] = 1
	}
	//最差时，也有一个信封
	res := 1
	for i := 1; i < len(envelopes); i++ {
		for j := 0; j < i; j++ {
			if envelopes[j][1] < envelopes[i][1] {
				dp[i] = max(dp[i], dp[j]+1)
			}
			res = max(res, dp[i])
		}
	}
	return res
}

func max(a, b int) int {
	if a > b {
		return a
	}
	return b
}

/*
*
9
3 4
2 3
4 5
1 3
2 2
3 6
1 2
3 2
2 4
结果
4
从里到外是 (1,2) (2,3) (3,4) (4,5)
*/
func main() {
	var num int
	fmt.Scanln(&num)
	arr := make([][]int, num)
	scanner := bufio.NewScanner(os.Stdin)
	for i := 0; i < num; i++ {
		scanner.Scan()
		str := scanner.Text()
		strs := strings.Split(str, " ")
		tmp := make([]int, 0)
		for _, val := range strs {
			ele, _ := strconv.Atoi(val)
			tmp = append(tmp, ele)
		}
		arr[i] = tmp
	}
	fmt.Println(solution(arr))
}