9行写完“过河卒”

#include <bits/stdc++.h>
using namespace std;
long long r, c, a, b, i, j, d, f[25][25];
int main(){
    for(memset(f, 0, sizeof(f)), cin >> r >> c >> a >> b, f[0][1] = i = 1, a++, b++, r++, c++; i <= r; i++)
        for(j = 1; j <= c; j++)
            f[i][j] = ((d = (i - a) * (i - a) + (j - b) * (j - b)) == 5 || d == 0) ? 0 : f[i - 1][j] + f[i][j - 1];
    cout << f[r][c] << '\n';
}