Sudoku variant · rules and tips

Classic Sudoku

The founding law, and the only one you need today. Every row, every column and every box holds each digit exactly once. No region repeats itself. Everything else in this app is a variation on that theme.

Get it onGoogle PlayPlay Classic Sudoku on the web
Professor Cryptic, the owl who teaches in the app
Professor Cryptic explains the rule

The Professor's tips

How do you solve Classic Sudoku?

01 / Warm up

Start on a 4 by 4 grid

  • Begin with the most crowded row or column. The fewer blanks it has, the fewer suspects you must interview.
  • A box holding three of its four digits has already confessed to the fourth. Look at the boxes before anything else.
  • Stuck? Pick one cell and ask what its row, its column and its box already contain. Whatever survives the questioning is your answer.
02 / Level up

Then try a 6 by 6 grid

  • The boxes are now 2 by 3, each holding 1 to 6. Notice how the new shape changes the way your eye travels.
  • Try cross-hatching. Take one digit, trace the rows and columns it already occupies, and see where it has room left. Usually it has very little.
  • Six digits make elimination quick. Rule out four and at most two remain. That is not a puzzle, that is a coin toss you can win.
  • Pay attention to the columns. In a 2 by 3 layout they are the constraint students forget, which is exactly why they solve things.

Start with a single square

Where can you play Classic Sudoku?

Classic Sudoku is one of the 17 variants in Cryptic, each with a lesson and unlimited puzzles.

Get it onGoogle PlayPlay on the web