网络路径走法

#include<iostream>
using namespace std;

long long  ans[25][25];

int main() {
    for (int i = 1; i <= 21; i++) {
        for (int j = 1; j <= 21; j++) {
            if (i == 1 && j == 1) {
                ans[i][j] = 1;
                continue;
            }
            ans[i][j] = ans[i - 1][j] + ans[i][j - 1];
        }
    }    
    cout << ans[21][21] << endl;
    return 0;
}