Determine if a 9x9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules:
<li>Each row must contain the digits <code>1-9</code> without repetition.</li>
<li>Each column must contain the digits <code>1-9</code> without repetition.</li>
<li>Each of the 9 <code>3x3</code> sub-boxes of the grid must contain the digits <code>1-9</code> without repetition.</li>
A partially filled sudoku which is valid.
The Sudoku board could be partially filled, where empty cells are filled with the character '.'.
Example 1:
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
Example 2:
Input:
[
["8","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: false
Explanation: Same as Example 1, except with the 5 in the top left corner being
modified to 8. Since there are two 8's in the top left 3x3 sub-box, it is invalid.
Note:
<li>A Sudoku board (partially filled) could be valid but is not necessarily solvable.</li>
<li>Only the filled cells need to be validated according to the mentioned rules.</li>
<li>The given board contain only digits <code>1-9</code> and the character <code>'.'</code>.</li>
<li>The given board size is always <code>9x9</code>.</li>