36. Valid Sudoku

Practice Valid Sudoku for free on NudgeCode: Medium, Array & Hash Table pattern. Write it in Python or JavaScript, run the tests in your browser, and ask for a hint when you are stuck.

board is a partly filled 9 x 9 Sudoku grid; empty cells are ".". Return true if no digit repeats within any row, any column, or any of the nine 3 x 3 boxes. Only the filled cells matter: you don't need to check whether the puzzle can be solved.

Example

board = [["5","3",".",".","7",".",".",".","."],
         ["6",".",".","1","9","5",".",".","."],
         [".","9","8",".",".",".",".","6","."],
         ["8",".",".",".","6",".",".",".","3"],
         ["4",".",".","8",".","3",".",".","1"],
         ["7",".",".",".","2",".",".",".","6"],
         [".","6",".",".",".",".","2","8","."],
         [".",".",".","4","1","9",".",".","5"],
         [".",".",".",".","8",".",".","7","9"]]
->  true

Change the top-left "5" to "8" and column 0 has two "8"s  ->  false

Constraints