Juegos III. Generador de Sudokus aleatorios.

Este generador crea un tablero de Sudoku completamente resuelto utilizando backtracking y luego elimina un número específico de celdas (en este caso 20) para crear el puzzle. Puedes ajustar el número de celdas eliminadas (NUM_REMOVES) para controlar la dificultad del sudoku generado.


Código Java (SudokuGenerator.java):

package sudokugenerator;

import java.util.Random;

public class SudokuGenerator {

    private static final int BOARD_SIZE = 9;
    private static final int SUB_GRID_SIZE = 3;
    private static final int NUM_REMOVES = 20;

    public static void main(String[] args) {
        int[][] board = generateSudoku();
        printBoard(board);
    }

    public static int[][] generateSudoku() {
        int[][] board = new int[BOARD_SIZE][BOARD_SIZE];
        populateBoard(board);
        removeCells(board);
        return board;
    }

    private static void populateBoard(int[][] board) {
        if (!solve(board, 0, 0)) {
            throw new IllegalStateException("No se pudo generar un sudoku válido.");
        }
    }

    private static boolean solve(int[][] board, int row, int col) {
        if (col == BOARD_SIZE) {
            col = 0;
            row++;
            if (row == BOARD_SIZE) {
                return true;
            }
        }

        if (board[row][col] != 0) {
            return solve(board, row, col + 1);
        }

        Random rand = new Random();
        for (int num : rand.ints(1, BOARD_SIZE + 1).distinct().limit(BOARD_SIZE).toArray()) {
            if (isValid(board, row, col, num)) {
                board[row][col] = num;
                if (solve(board, row, col + 1)) {
                    return true;
                }
            }
        }

        board[row][col] = 0;
        return false;
    }

    private static boolean isValid(int[][] board, int row, int col, int num) {
        for (int i = 0; i < BOARD_SIZE; i++) {
            if (board[row][i] == num || board[i][col] == num) {
                return false;
            }
        }

        int r = row - row % SUB_GRID_SIZE;
        int c = col - col % SUB_GRID_SIZE;
        for (int i = r; i < r + SUB_GRID_SIZE; i++) {
            for (int j = c; j < c + SUB_GRID_SIZE; j++) {
                if (board[i][j] == num) {
                    return false;
                }
            }
        }

        return true;
    }

    private static void removeCells(int[][] board) {
        Random rand = new Random();
        for (int i = 0; i < NUM_REMOVES; i++) {
            int row = rand.nextInt(BOARD_SIZE);
            int col = rand.nextInt(BOARD_SIZE);
            board[row][col] = 0;
        }
    }

    private static void printBoard(int[][] board) {
        for (int i = 0; i < BOARD_SIZE; i++) {
            for (int j = 0; j < BOARD_SIZE; j++) {
                System.out.print(board[i][j] + " ");
            }
            System.out.println();
        }
    }
}


Resultado:

2 7 9 4 3 8 1 5 0
3 4 1 0 7 6 2 8 0
6 8 5 2 1 0 7 3 4
9 0 8 3 0 7 0 6 0
4 1 3 9 6 0 8 7 2
5 0 0 1 0 2 4 9 3
7 9 2 6 0 1 3 4 0
0 3 6 7 2 4 9 1 5
1 5 4 0 9 3 0 2 7