Java 代码

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;

public class Main {
    private static int N = 10;
    private static char[][] g = new char[N][N];
    private static boolean[][] row = new boolean[N][N], col = new boolean[N][N];
    private static boolean[][][] cell = new boolean[N][N][N];
    private static BufferedReader reader;
    private static PrintWriter writer;

    private static boolean dfs(int x, int y) {
        if (y == 9) {
            x ++;
            y = 0;
        }
        if (x == 9) {
            for (int i = 0; i < 9; i ++) writer.println(g[i]);
            writer.flush();
            return true;
        }

        // 当前不是空搜索下一个
        if (g[x][y] != '.') return dfs(x, y + 1);

        // 遍历数独中的数字1-9
        for (int i = 1; i <= 9; i ++) {
            if (!row[x][i] && !col[y][i] && !cell[x / 3][y / 3][i]) {
                g[x][y] = (char) (i + '0');
                row[x][i] = col[y][i] = cell[x / 3][y / 3][i] = true;
                if (dfs(x, y + 1) == true) return true; // 剪枝
                // 还原
                row[x][i] = col[y][i] = cell[x / 3][y / 3][i]= false;
                g[x][y] = '.';
            }
        }

        return false;
    }

    public static void main(String[] args) throws IOException {
        reader = new BufferedReader(new InputStreamReader(System.in));
        writer = new PrintWriter(System.out);

        for (int i = 0; i < 9; i ++) {
            g[i] = reader.readLine().toCharArray();
        }

        reader.close();

        for (int i = 0; i < 9; i ++) {
            for (int j  = 0; j < 9; j ++) {
                if (g[i][j] != '.') {
                    int t = g[i][j] - '0'; // 转换坐标
                    row[i][t] = col[j][t] = cell[i / 3][j / 3][t] = true;
                }
            }
        }

        dfs(0, 0);

        writer.flush();
        writer.close();
    }
}