Solution: Valid Sudoku
Understand how to verify the validity of a Sudoku board by scanning cells once while tracking digits in rows, columns, and 3x3 sub-boxes with hash maps. This lesson teaches a clear approach to constraint checking without backtracking, helping you implement an efficient constant-time solution.
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Statement
Given a 9 × 9 Sudoku board, determine whether it is valid. A board is considered valid if all of the following conditions hold (considering only the filled cells):
Each row contains the digits
1–9at most once.Each column contains the digits
1–9at most once.Each of the nine 3 × 3 sub-boxes contains the digits
1–9at most once.
You do not need to check whether the Sudoku is solvable; only whether the current filled entries obey these rules.
Note: A partially filled Sudoku board can be valid even if it is not necessarily solvable. You only need to verify that the filled cells adhere to the given rules.
Constraints:
board.length...