动态规划

 1 package pro20190110;
 2 
 3 import java.util.Scanner;
 4 
 5 public class Main {
 6     public static void main(String[] args) {
 7         Scanner in = new Scanner(System.in);
 8         int n = in.nextInt();
 9         int sum = in.nextInt();
10         int[] arr = new int[n];
11         for (int i = 0; i < n; i++) {
12             arr[i] = in.nextInt();
13         }
14 
15         //dp[i][j] 存放第i个数字之前组合和为j的方案个数
16         int[][] dp = new int[n + 1][sum + 1];
17         
18         for (int i = 0; i <= n; i++) {
19             dp[i][0] = 1;
20         }
21 
22         for (int j = 1; j <= sum; j++) {
23             for (int i = 0; i < n; i++) {
24                 if (j - arr[i] < 0) {
25                     //如果小于0 则等于该列上一行
26                     dp[i + 1][j] = dp[i][j];
27                 } else {
28                     //等于该列上一行加上上一行中差值对应列的元素和
29                     dp[i + 1][j] = dp[i][j] + dp[i][j - arr[i]];
30                 }
31             }
32         }
33 
34 
35         System.out.println(dp[n][sum]);
36     }
37 }