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Validate 9x9 grid in one pass

AmazonSoftware Engineer · Onsite
MediumSoftware EngineerOnsiteCoding & Algorithms

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This interview question evaluates algorithm design, data structures, correctness, complexity, edge cases, and implementation details in a realistic interview setting. A strong answer for Validate 9x9 grid in one pass states assumptions, handles edge cases, explains trade-offs, and shows how to validate the result clearly.

Given a partially filled 9x9 board using digits '1'–'9' and '.' for empty cells, determine whether the current configuration is valid under Sudoku rules (no duplicates per row, column, or 3x3 sub-box). Provide a one-pass algorithm that detects conflicts during a single scan, describe your data structures (e.g., bitmasks or hash sets), and analyze time and space complexity.