hdu 1267 下沙的沙子有几粒？

#include<stdio.h>typedef long long LL;const int N=21;LL dp[N][N];//i个H j个Dint main(){dp[0][0]=1;for(int i=0;i<N;i++){for(int j=0;j<N;j++){if(dp[i][j]==0) continue;dp[i+1][j]+=dp[i][j];if(j+1<=i)//D不大于Hdp[i][j+1]+=dp[i][j];}}int n,m;while(~scanf("%d %d",&m,&n)){printf("%I64d\n",dp[m][n]);}}