OpenJudge Bailian 2755 神奇的口袋 DP

#include <iostream>
#include <cstring>
#include <cstdio>
#include <algorithm>
#include <queue>
#include <vector>
#include <iomanip>
#include <math.h>
#include <map>
using namespace std;
#define FIN     freopen("input.txt","r",stdin);
#define FOUT    freopen("output.txt","w",stdout);
#define INF     0x3f3f3f3f
#define INFLL   0x3f3f3f3f3f3f3f
#define lson    l,m,rt<<1
#define rson    m+1,r,rt<<1|1
typedef long long LL;
typedef pair<int,int> PII;

int a[25];
int dp[100][100];

int main()
{
    //FIN
    int n;
    while(~scanf("%d", &n)){
        for(int i = 1; i <= n; i ++){
            scanf("%d", &a[i]);
            dp[i][0] = 1;
        }
        dp[0][0] = 1;
        for(int i = 1; i <= n; i ++){
            for(int j = 1; j <= 40; j ++){
                dp[i][j] = dp[i - 1][j];
                if(j >= a[i]){
                    dp[i][j] += dp[i - 1][j - a[i]];
                }
            }
        }
        printf("%d\n", dp[n][40]);

    }
}