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.
- Only the filled cells need to be validated according to the mentioned rules.
This problem asks you to verify whether a partially filled 9 x 9 Sudoku board is valid. You only need to check the filled cells, ensuring there are no repeated digits in any row, column, or 3 x 3 sub-box. The board does not need to be solvable, only consistent with the Sudoku rules so far. A common solution is to scan the grid once while using sets or boolean markers for rows, columns, and boxes, and return false as soon as a duplicate is found.
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