Daily Interview Pro Hi, here’s your problem today. This problem was recently asked by Facebook:

A Sudoku board is a 9x9 grid, where each row, column and each 3x3 subbox contains the number from 1-9. Here’s an example of a Sudoku board.

-------------
|534|678|912|
|672|195|348|
|198|342|567|
|------------
|859|761|423|
|426|853|791|
|713|924|856|
|------------
|961|537|284|
|287|419|635|
|345|286|179|
|------------

Given a 9x9 board, determine if it is a valid Sudoku board. The board may be partially filled, where an empty cell will be represented by the space character ’ ’.

Here’s an example and some starting code:

def validate_sudoku(board):
  # Fill this in.

board = [
    [5, ' ', 4, 6, 7, 8, 9, 1, 2],
    [6, ' ', 2, 1, 9, 5, 3, 4, 8],
    [1,   9, 8, 3, 4, 2, 5, 6, 7],
    [8,   5, 9, 7, 6, 1, 4, 2, 3],
    [4,   2, 6, 8, 5, 3, 7, 9, 1],
    [7,   1, 3, 9, 2, 4, 8, 5, 6],
    [9,   6, 1, 5, 3, 7, 2, 8, 4],
    [2,   8, 7, 4, 1, 9, 6, 3, 5],
    [3,   4, 5, 2, 8, 6, 1, 7, 9],
]

print(validate_sudoku(board))
# True