AtCoder Beginner Contest 196 D Hanjo

原题链接
用dfs爆搜即可

#include <iostream>

using namespace std;

const int N = 20;

int ans = 0;

bool st[N][N];
int n, m, a, b;
int dir[2][2] = {0, 1, 1, 0};


void dfs(int u, int x, int y) {

    if (u == a + 1) {
        ans ++;
        return ;
    }

    for (int i = x; i < n; i ++)
    for (int j = (i == x ? y : 0); j < m; j ++) {
        if (!st[i][j]) {
            st[i][j] = 1;
            for (int k = 0; k < 2; k ++) {
                int a = i + dir[k][0], b = j + dir[k][1];
                if (a < 0 || a >= n || b < 0 || b >= m || st[a][b]) continue;
                st[a][b] = 1;
                if (j == m - 1)
                dfs(u + 1, i + 1, 0);
                else dfs(u + 1, i, j + 1);
                st[a][b] = 0;
            }
            st[i][j] = 0;
        }
    }
}

int main() {
    cin >> n >> m >> a >> b;
    dfs(1, 0, 0);
    cout << ans << endl;
    return 0;
}