Given a 9 × 9 Sudoku board, determine whether it is valid. A board is considered valid if all of the following conditions hold (considering only the filled cells):

• Each row contains the digits 1–9 at most once.

• Each column contains the digits 1–9 at most once.

• Each of the nine 3 × 3 sub-boxes contains the digits 1–9 at most once.

You do not need to check whether the Sudoku is solvable; only whether the current filled entries obey these rules.

Note:A partially filled Sudoku board can be valid even if it is not necessarily solvable. You only need to verify that the filled cells adhere to the given rules.

Constraints:

• board.length $= 9$

• board[i].length $= 9$

• board[i][j] is a digit or ..

Let’s take a moment to make sure you’ve correctly understood the problem. The quiz below helps you check if you’re solving the correct problem:

We have a game for you to play. Rearrange the logical building blocks to develop a clearer understanding of how to solve this problem.

Implement your solution in the following coding playground.