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Grokking the Coding Interview Patterns in C#

Valid Sudoku

Explore how to determine the validity of a partially filled Sudoku board by verifying that no digit repeats in any row, column, or 3x3 sub-box. Learn to apply hash maps in C# to efficiently implement these checks and understand the problem constraints without needing to solve the puzzle.

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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.

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