恢复现场1

import java.util.*;

public class Main {
    static int n,m,x,y;
    static int N = 15;
    static int res;
    static int[][] map = new int[N][N];
    static boolean[][] st = new boolean[N][N];
    static int[] dx = {-2,-1,1,2,2,1,-1,-2};
    static int[] dy = {1,2,2,1,-1,-2,-2,-1};//偏移量

    public static void dfs(int x,int y,int cnt) {
        if (cnt == n * m) { //终止条件
            res ++;
            return;
        }

        st[x][y] = true;//标记为走过

        for (int i = 0;i < 8;i ++) {
            int a = x + dx[i];
            int b = y + dy[i];
            if (a < 0 || b < 0 || a >= n || b >= m) continue;//判断是否超出边界
            if (st[a][b]) continue;//判断是否走过

            dfs(a,b,cnt + 1);
        }
        st[x][y] = false;//恢复现场
    }
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int t = sc.nextInt();
        while (t -- > 0) {
            n = sc.nextInt();
            m = sc.nextInt();
            x = sc.nextInt();
            y = sc.nextInt();

            res = 0;
            for (int i = 0;i < n;i ++) 
                for (int j = 0;j < m;j ++)
                    st[i][j] = false;

            dfs(x,y,1);

            System.out.println(res);
        }
    }
}

恢复现场2

//二刷
import java.util.*;

public class Main {
    static int n,m,x,y;
    static int N = 15;
    static int res;
    static int[][] map = new int[N][N];
    static boolean[][] st = new boolean[N][N];
    static int[] dx = {-2,-1,1,2,2,1,-1,-2};
    static int[] dy = {1,2,2,1,-1,-2,-2,-1};//偏移量

    public static void dfs(int x,int y,int cnt) {
        if (cnt == n * m) { //终止条件
            res ++;
            return;
        }

        for (int i = 0;i < 8;i ++) {
            int a = x + dx[i];
            int b = y + dy[i];
            if (a < 0 || b < 0 || a >= n || b >= m) continue;//判断是否超出边界
            if (st[a][b]) continue;//判断是否走过

            st[a][b] = true;//标记走过
            dfs(a,b,cnt + 1);
            st[a][b] = false;//恢复现场
        }
    }
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int t = sc.nextInt();
        while (t -- > 0) {
            n = sc.nextInt();
            m = sc.nextInt();
            x = sc.nextInt();
            y = sc.nextInt();

            res = 0;
            for (int i = 0;i < n;i ++) 
                for (int j = 0;j < m;j ++)
                    st[i][j] = false;
            st[x][y] = true;

            dfs(x,y,1);

            System.out.println(res);
        }
    }
}