Codeforces 478D Red-Green Towers

http://codeforces.com/problemset/problem/478/D

思路:dp：f[i][j]代表当前第i层，用了j个绿色方块的方案数，用滚动数组，还有，数组清零的时候一定要用memset，不然for的常数太大。。

 #include<cstdio>
 #include<cmath>
 #include<algorithm>
 #include<cstring>
 #include<iostream>
 const int Mod=;
 int n,m,sum[],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();
     for (int i=;i<=;i++)
      sum[i]=sum[i-]+i;
     f[][]=;
     int i;
     for (i=;;i++){
         if (sum[i]>n+m) break;
         memset(f[i%],,sizeof f[i%]);
         for (int j=;j<=sum[i]&&j<=m;j++){
             if (sum[i]-j<=n) (f[i%][j]+=f[(i-)%][j])%=Mod;
             if (sum[i]-j<=n&&j>=i) (f[i%][j]+=f[(i-)%][j-i])%=Mod;
         }
     }
     int ans=;
     for (int j=;j<=m;j++)
      ans=(ans+f[(i-)%][j])%Mod;
     printf("%d\n",ans);
     return ;
 }