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 valid Sudoku board (partially filled) is not necessarily solvable. Only the filled cells need to be validated.
The rule of Sudoku: 1. Each row must have number 1-9 occurring only once; 2. Each col must have number 1-9 occurring only once; 3. The number 1-9 must occur just once in each of the sub-boxes. (Updating...)