数字和为sum的方法数（动态规划）

 1 import java.util.Scanner;
 2 
 3 /** 
 4  * @author Dell
 5  *
 6  */
 7 public class Main {
 8 static public long dp[][];
 9 public static void main(String[] args) {
10     Scanner sc = new Scanner(System.in);
11     int n = sc.nextInt();
12     int sum = sc.nextInt();
13     int [] p = new int[(int) (n+1)];
14     /**
15      * 循环全部从1开始
16      * 
17      */
18     for (int i= 1; i < p.length; i++) {
19         p[i] = sc.nextInt();
20     }
21     dp = new long[n+1][sum+1];
22     for (int i = 0; i <n+1; i++) {
23         for (int j = 0; j <sum+1; j++) {
24             dp[i][j] = 0;
25         }
26     }
27     dp[0][0] = 1; //初始化 0 行
28     for (int i = 1; i <=n; i++) { 
29         for (int j = 0; j <=sum; j++) { // 0-sum列
30             long k;
31             if (j-p[i]<0) {
32                 k = 0;
33             }else {
34                 k = dp[i-1][j-p[i]];
35             }
36             dp[i][j] = dp[i-1][j]+k;
37         }
38     }
39     System.out.println(dp[n][sum]);
40 }
41 }