算法

(暴搜)

由于 $hw \leqslant 16$，所以爆搜即可。

C++ 代码

#include <bits/stdc++.h>

using std::cin;
using std::cout;
using ll = long long;

int h, w;
int used[16][16];

ll dfs(int i, int j, int a, int b) {
    if (a < 0 || b < 0) return 0;
    if (j == w) j = 0, ++i;
    if (i == h) return 1;
    if (used[i][j]) return dfs(i, j + 1, a, b);
    ll res = 0;
    used[i][j] = true;
    res += dfs(i, j + 1, a, b - 1);
    if (j + 1 < w and !used[i][j + 1]) {
        used[i][j + 1]= true;
        res += dfs(i, j + 1, a - 1, b);
        used[i][j + 1] = false;
    }
    if (i + 1 < h and !used[i + 1][j]) {
        used[i + 1][j]= true;
        res += dfs(i, j + 1, a - 1, b);
        used[i + 1][j] = false;
    }
    used[i][j] = false;
    return res;
}

int main() {
    cin >> h >> w;
    int a, b;
    cin >> a >> b;

    cout << dfs(0, 0, a, b) << '\n';

    return 0;
}