Codeforces 543A Writing Code

http://codeforces.com/problemset/problem/543/A

题目大意：n个人，一共要写m行程序，每个程序员每行出现的bug数为ai，要求整个程序出现的bug数不超过b的方案数.

思路:f[i][j]代表第m行，j个bug的方案数，n^3转移

 #include<cstdio>
 #include<cmath>
 #include<iostream>
 #include<algorithm>
 #include<cstring>
 int n,m,b,Mod;
 int a[],f[][];
 int read(){
     int t=,f=;char ch=getchar();
     while (ch<''||ch>''){if (ch=='-') f=-;ch=getchar();}
     while (''<=ch&&ch<='') {t=t*+ch-'';ch=getchar();}
     return t*f;
 }
 int main(){
     n=read();m=read();b=read();Mod=read();
     for (int i=;i<=n;i++) a[i]=read();
     f[][]=;
     for (int i=;i<=n;i++)
      for (int j=;j<=m;j++)
       for (int k=b;k>=;k--)
         if (k>=a[i])
             f[j][k]=(f[j][k]+f[j-][k-a[i]])%Mod;
     int ans=;
     for (int i=;i<=b;i++)
      ans=(ans+f[m][i])%Mod;
     printf("%d\n",ans);
 }