Valid Sudoku

Determine if a Sudoku is valid, according to: Sudoku Puzzles - The
Rules.

The Sudoku board could be partially filled, where empty cells are
filled with the character '.'.

A partially filled sudoku which is valid.

Note:
A valid Sudoku board (partially filled) is not necessarily solvable.
Only the filled cells need to be validated.
Add another solution

Add the notable and efficient brute force method