[python] sudoku 만들기

# sudoku using python

def is_valid_move(board, row, col, num):
    """
    Check if placing 'num' at position (row, col) is a valid move.
    """
    # Check the row
    if num in board[row]:
        return False

    # Check the column
    if num in [board[i][col] for i in range(9)]:
        return False

    # Check the 3x3 subgrid
    start_row, start_col = 3 * (row // 3), 3 * (col // 3)
    for i in range(start_row, start_row + 3):
        for j in range(start_col, start_col + 3):
            if board[i][j] == num:
                return False

    return True

def solve_sudoku(board):
    """
    Solve the Sudoku puzzle using backtracking.
    """
    empty_cell = find_empty_cell(board)

    if not empty_cell:
        # Puzzle is solved
        return True

    row, col = empty_cell

    for num in range(1, 10):
        if is_valid_move(board, row, col, num):
            board[row][col] = num

            if solve_sudoku(board):
                return True

            # If the current placement doesn't lead to a solution, backtrack
            board[row][col] = 0

    # No valid move found, need to backtrack
    return False

def find_empty_cell(board):
    """
    Find an empty cell in the Sudoku grid.
    """
    for i in range(9):
        for j in range(9):
            if board[i][j] == 0:
                return (i, j)
    return None

def print_board(board):
    """
    Print the Sudoku grid.
    """
    for i in range(9):
        if i % 3 == 0 and i != 0:
            print("- - - - - - - - - - - -")
        for j in range(9):
            if j % 3 == 0 and j != 0:
                print("|", end=" ")
            print(board[i][j], end=" ")
        print()

# Example Sudoku puzzle (0 represents empty cells)
sudoku_board = [
    [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_board(sudoku_board)
print("\nSolving...\n")

if solve_sudoku(sudoku_board):
    print("Sudoku Solution:")
    print_board(sudoku_board)
else:
    print("No solution exists.")