Valid Sudoku (#36)

Determine if a 9 x 9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules:

Each row must contain the digits 1-9 without repetition.
Each column must contain the digits 1-9 without repetition.
Each of the nine 3 x 3 sub-boxes of the grid must contain the digits 1-9 without repetition.

Note: A Sudoku board (partially filled) could be valid but is not necessarily solvable. You only need to validate the given-state of the board.

Company Tags: Amazon

Core Concept: Hashing, Matrix