动规解法

#include<bits/stdc++.h>
using namespace std;
int dp[25][25];
int main(){
    dp[1][1] = 1;
    int n,m; cin >> n >> m;
    for(int i = 1;i <= n;i++){
        for(int j = 1;j <= m;j++){
            if(i == 1 && j == 1) continue;
            dp[i][j] = dp[i][j - 1] + dp[i - 1][j];
        }
    }
    cout << dp[n][m];
    return 0;
}