题解 | #购物单#

import java.util.Scanner;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
  public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        // 注意 hasNext 和 hasNextLine 的区别
        while (in.hasNextInt()) { // 注意 while 处理多个 case
            int N = in.nextInt();
            int m = in.nextInt();
            Goods[] goods = new Goods[m];
            for (int i = 0; i < m; i++) {
                goods[i] = new Goods();
            }
            for (int i = 0; i < m; i++) {
                int v = in.nextInt();
                int p = in.nextInt();
                int q = in.nextInt();
                goods[i].v = v;
                goods[i].p = p * v;
                if (q > 0) {
                    goods[i].isMain = false;
                    if (goods[q - 1].a1 == null) {
                        goods[q - 1].a1 = goods[i];
                    } else {
                        goods[q - 1].a2 = goods[i];
                    }
                } else {
                    goods[i].isMain = true;
                }
            }
            // 五种情况：根据主件来，因为即使买附件也得必买主件。
            // 1. 不买主件i
            // 2. 只买主件i
            // 3. 买主件i及其附件a1
            // 4. 买主件i及其附件a2
            // 5. 买主件i及其附件a1\a2
            int[][] dp = new int[m + 1][N + 1];
            for (int i = 1; i <= m; i++) {
                for (int j = 1; j <= N; j++) {
                    dp[i][j] = dp[i - 1][j];
                    if (!goods[i - 1].isMain){
                        continue;
                    }
                    if(j >= goods[i - 1].v){
                        dp[i][j] = Math.max(dp[i-1][j], dp[i - 1][j - goods[i - 1].v] + goods[i - 1].p);
                    }
                        
                        if (goods[i - 1].a1 != null&&j>=goods[i - 1].v + goods[i - 1].a1.v) {
                            dp[i][j] = Math.max(dp[i][j], dp[i - 1][j - goods[i - 1].v - goods[i - 1].a1.v]
                                    + goods[i - 1].p + goods[i - 1].a1.p);
                        }
                        if (goods[i - 1].a2 != null&&j>=goods[i - 1].v + goods[i - 1].a2.v) {
                            dp[i][j] = Math.max(dp[i][j], dp[i - 1][j - goods[i - 1].v - goods[i - 1].a2.v]
                                    + goods[i - 1].p + goods[i - 1].a2.p);
                        }
                        if (goods[i - 1].a2 != null && goods[i - 1].a1 != null&&j>=goods[i - 1].v + goods[i - 1].a1.v + goods[i - 1].a2.v) {
                            dp[i][j] = Math.max(dp[i][j],
                                    dp[i - 1][j - goods[i - 1].v - goods[i - 1].a1.v - goods[i - 1].a2.v]
                                            + goods[i - 1].p + goods[i - 1].a1.p + goods[i - 1].a2.p);
                        }
                    
                }
            }
            System.out.println(dp[m][N]);
        }
    }
}

class Goods {
    int v;
    int p;
    boolean isMain;

    Goods a1;
    Goods a2;
}