2019 nowcoder 19第一场 E dp

#include <bits/stdc++.h>
using namespace std;
const int maxn = 2e3+10;
int dp[maxn][maxn];
int n,m;
const int mod = 1e9+7;
int main()
{
	while(scanf("%d %d",&n,&m)==2){
		for(int i=0;i<=n+m;i++)
			for(int j=0;j<=n+m;j++){
				dp[i][j] = 0;
			} 
		dp[0][0] = 1;
		for(int i=0;i<=n+m;i++){
			for(int j=0;j<=n+m;j++){
				if(i<n+j)
					dp[i+1][j] = (dp[i][j] + dp[i+1][j])%mod;
				if(j<m+i)
					dp[i][j+1] = (dp[i][j] + dp[i][j+1])%mod;
			}
		}
		printf("%d\n",dp[n+m][n+m]);
	} 
	
	return 0;
 }