Valid Sudoku
Medium · Hashing · about 15 minutes
Asked at Apple, Amazon, Bloomberg, Meta, Microsoft, Google, Uber.
Check a 9 × 9 Sudoku grid that is only partly filled in. Ignore the blanks and confirm that no digit from 1 to 9 repeats
- within any row,
- within any column, or
- within any of the nine 3 × 3 boxes.
Each row of the grid arrives as a 9-character string, and '.' marks a blank. The grid only has to obey these rules; it does not have to be solvable.