How to play
Hard grids start with only 27 givens. Expect long stretches where notes and pairs are the only way forward.
- Fill every row, column and 3×3 box with the digits 1 to 9, each used once.
- Tap a cell, then tap a number. On a computer you can type digits and move with the arrow keys.
- Switch on Notes (or press N) to pencil in candidates. Placing a digit clears it from the notes in the same row, column and box.
- Repeated digits turn red straight away. Check marks any cell that differs from the solution; Hint fills one cell for you.
Tips for hard grids
- Naked pairs: two cells in a unit with the same two candidates let you remove those digits from the rest of the unit.
- Pointing pairs: if a digit in a box can only sit in one row, remove it from that row outside the box.
About sudoku
Sudoku is a logic puzzle played on a 9×9 grid divided into nine 3×3 boxes. The goal is to fill every row, every column and every box with the digits 1 to 9, each exactly once. Some digits, called givens, are already placed, and the fewer givens a grid has, the harder it usually is.
The modern puzzle first appeared as “Number Place” in Dell Magazines in 1979 and is credited to the American puzzle maker Howard Garns. The Japanese publisher Nikoli popularised it in the 1980s and gave it the name Sudoku.
Frequently asked questions
- How many clues does a hard sudoku have?
- Hard grids here start with 27 givens.
- Do hard sudoku puzzles need guessing?
- No. Each grid has exactly one solution, so it can be reached by logic, although hard grids need techniques such as pairs and pointing pairs.