33. Valid Sudoku
Determine if a 9 x 9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules: 1. Each row must contain the digits 1-9 without repetition. 2. Each column must contain the digits 1-9 without repetition. 3. 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. - Only the filled cells need to be validated according to the mentioned rules.
Examples
Input: [["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"]]
Output: true
Explanation: No digit repeats within any row, column, or 3x3 box.
Constraints
- board.length == 9
- board[i].length == 9
- board[i][j] is a digit 1-9 or '.'.
Run checks all cases above. Submit evaluates all test cases.