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Grokking the Coding Interview Patterns in Go

Solution: Valid Sudoku

Explore how to determine the validity of a partially filled 9x9 Sudoku board by efficiently checking digit constraints across rows, columns, and sub-boxes. Understand the use of hash maps to track seen numbers in constant time, ensuring compliance with Sudoku rules without solving the puzzle. This lesson strengthens your ability to apply hash maps for constraint checking in coding interviews.

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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 1–9 at most once.

  • Each column contains the digits 1–9 at most once.

  • Each of the nine 3 × 3 sub-boxes contains the digits 1–9 at 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 =9= 9 ...