class Sudoku {
    grid = null;
    size = 9;
    boxSize = 3;

    Sudoku(this, puzzle) {
        this.grid = puzzle;
    }

    isValid(this, row, col, num) {
        for (i = 0; i < 9; i++) {
            if (this.grid[row * 9 + i] == num) {
                return 0;
            }
        }
        for (i = 0; i < 9; i++) {
            if (this.grid[i * 9 + col] == num) {
                return 0;
            }
        }
        boxRow = (row / 3) * 3;
        boxCol = (col / 3) * 3;
        for (i = 0; i < 3; i++) {
            for (j = 0; j < 3; j++) {
                idx = (boxRow + i) * 9 + (boxCol + j);
                if (this.grid[idx] == num) {
                    return 0;
                }
            }
        }
        return 1;
    }

    solve(this) {
        for (row = 0; row < 9; row++) {
            for (col = 0; col < 9; col++) {
                idx = row * 9 + col;
                if (this.grid[idx] == 0) {
                    for (num = 1; num <= 9; num++) {
                        if (this.isValid(row, col, num)) {
                            this.grid[idx] = num;
                            if (this.solve()) {
                                return 1;
                            }
                            this.grid[idx] = 0;
                        }
                    }
                    return 0;
                }
            }
        }
        return 1;
    }

    printGrid(this) {
        for (row = 0; row < 9; row++) {
            line = "";
            for (col = 0; col < 9; col++) {
                line += str(this.grid[row * 9 + col]);
                if (col < 8) {
                    line += " ";
                }
                if (col == 2 || col == 5) {
                    line += "| ";
                }
            }
            print(line);
            if (row == 2 || row == 5) {
                print("------+-------+------");
            }
        }
    }
}

puzzle = {
    5, 3, 0, 0, 7, 0, 0, 0, 0,
    6, 0, 0, 1, 9, 5, 0, 0, 0,
    0, 9, 8, 0, 0, 0, 0, 6, 0,
    8, 0, 0, 0, 6, 0, 0, 0, 3,
    4, 0, 0, 8, 0, 3, 0, 0, 1,
    7, 0, 0, 0, 2, 0, 0, 0, 6,
    0, 6, 0, 0, 0, 0, 2, 8, 0,
    0, 0, 0, 4, 1, 9, 0, 0, 5,
    0, 0, 0, 0, 8, 0, 0, 7, 9
};

print("Sudoku Puzzle:");
print("==============");
sudoku = new Sudoku(puzzle);
sudoku.printGrid();

print("");
print("Solving...");
print("");

if (sudoku.solve()) {
    print("Solution:");
    print("=========");
    sudoku.printGrid();
} else {
    print("No solution exists");
}