Sudoku

How do you play Sudoku?

Fill a 9×9 grid so every row, column, and 3×3 box contains the digits 1–9 exactly once. No math required — only logic.

What are pencil marks in Sudoku?

Small candidate numbers you write in cells to track possibilities. Eliminating candidates is the core of advanced Sudoku solving.

What is the fastest Sudoku solving technique?

Start with 'naked singles' (cells with only one possible candidate). Then find 'hidden singles' (a digit that can only go in one cell within a row/column/box).