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Grokking the Coding Interview Patterns

Valid Sudoku

Explore how to determine the validity of a 9x9 Sudoku board by applying hash map concepts. Learn to verify that each row, column, and 3x3 sub-box contains unique digits without duplication. This lesson develops problem-solving skills in hash maps and pattern recognition critical for 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.

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