Arctic SudokuLevels
The level isn't set by how many digits are given, but by the hardest technique you need – plus a requirement for how many hard steps the board contains. It's the same model as the well-known program HoDoKu.
Extra easy
Hidden singles only. 40–46 digits given.
Easy
Hidden and naked singles. 32–38 digits given.
Medium
+ locked candidates (pointing/claiming), pairs and triples.
Hard
+ X-wing, Y-wing, swordfish, XYZ-wing, W-wing, skyscraper/kite and simple colouring.
Expert
+ X-chains, XY-chains, AIC and jellyfish – and plenty of hard steps.
| Level | Sudoku | Killer Sudoku |
|---|---|---|
| Extra easy | Hidden singles only. 40–46 digits given. | Cage combinations and the 45 rule on a single cell. 25 digits given, cages of 2–3 cells. |
| Easy | Hidden and naked singles. 32–38 digits given. | As Extra easy, with 15 digits given. |
| Medium | + locked candidates (pointing/claiming), pairs and triples. | As Easy, with 5 digits given. |
| Hard | + X-wing, Y-wing, swordfish, XYZ-wing, W-wing, skyscraper/kite and simple colouring. | + locked candidates inside cages and the 45 rule across several cells. No digits given, cages of 2–4 cells. |
| Expert | + X-chains, XY-chains, AIC and jellyfish – and plenty of hard steps. | + innies/outies, cage splitting, min/max sums and chains through cages. Cages of up to 5 cells. |
Every board can be solved without guessing. The app doesn't use techniques that assume the solution is unique, and there are no trial-and-error chains.