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Determine if a 9x9 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 3x3 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.
A 2D array board, where board[i][j] is a character '1'-'9' or '.' representing empty cells.
Return true if the board is valid according to Sudoku rules, otherwise return false.
board.length == 9; board[i].length == 9; board[i][j] is a digit '1'-'9' or '.'
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
Explanation
The given board is a valid Sudoku board.