背包问题

import java.util.*;
public class Main{
    public static final int ASD = 1000000007;

    public static void main(String[] args){

        Scanner sc = new Scanner(System.in);
        int k=sc.nextInt();
        int a=sc.nextInt();
        int x=sc.nextInt();
        int b=sc.nextInt();
        int y=sc.nextInt();
        int sum = 0;
        //k=17;a=5;x=79;b=4;y=66;
        //k=205;a=1;x=92;b=4;y=92;
        //3615040
        sc.close();

        int[] n = new int[x + y];
        int[] e = new int[x + y];
        for(int i = 0; i < n.length; i++){
            if(i < x){
                e[i] = a;
            }
            else{
                e[i] = b;
            }
            n[i] = 0;
        }

        sum  = dp(n, e, k, 0, -1);
        System.out.println(sum);
    }

    public static int dp(int[] n, int[] e, int k, int sum, int yn){

        if(meetRequire(n, e, k) == 2){ //已经超过k时之后的分支不用判断。
            return sum;
        }

        yn = yn + 1;

        n[yn] = 1;
        if(yn < n.length-1){
            sum = dp(n, e, k, sum, yn);
        }

        if(meetRequire(n, e, k) == 1){
            sum = sum + 1;
        }
        System.out.println("" + n[0] + n[1] + n[2] + n[3] + n[4] + n[5] + " " + sum);

        n[yn] = 0;
        if(yn < n.length-1){
            sum = dp(n, e, k, sum, yn);
        }


        return sum;
    }


    public static int meetRequire(int[] n, int[] e, int k){
        int s = 0;
        for(int i = 0; i < n.length; i++){
            if(n[i] == 1){
                s  = s + e[i];
            }
        }
        if(s < k){
            //System.out.println("" + n[0] + n[1] + n[2] + n[3] + n[4] + n[5] );
            return 0;
        }
        else if(s == k){
            //System.out.println("" + n[0] + n[1] + n[2] + n[3] + n[4] + n[5] );
            return 1;
        }
        else{
            return 2;
        }
    }
}

递归遍历二叉树的方法- -|||

分支界限法=。=||

30%case通过率，更蠢了。。。

reference

https://www.bilibili.com/video/av50202822?from=search&seid=13676114442420163856