All Sudoku Variants
9×9 · Constraint

Pencilmark Sudoku

Also known as Sukaku

There are no given digits — instead every cell shows a small list of candidates, and you choose one digit per cell to build a valid Sudoku.

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An example Pencilmark (Sukaku) puzzle: cells carry candidate lists instead of givens — choose one digit per cell to make a valid Sudoku.

Pencilmark Sudoku — also called Sukaku — replaces the usual given digits with candidate lists. Every cell shows the small set of digits it is allowed to take, and your job is to pick exactly one from each so that the finished grid is a proper Sudoku.

The rule: choose one candidate per cell

Read each cell's list as "the answer here is one of these". The ordinary Sudoku rules do the rest: every row, column and box must end up holding 1–9 once, which forces a single choice out of each list.

Solving strategy

  • Hunt the singletons. A cell whose list has only one digit is already solved.
  • Use the lists as candidates. They are literally the pencil marks you would make yourself — so every standard technique (naked pairs, hidden singles) applies at once.
  • Eliminate across units. Placing a digit strikes it from the lists of its row, column and box.

Common mistakes

  • Treating a list as a multi-digit answer. Exactly one candidate from each cell survives.
  • Ignoring the given lists. A digit not in a cell's list can never go there.
  • Forgetting ordinary Sudoku. The final grid must still hold 1–9 in every row, column and box.

Can I play it here?

Not yet — Pencilmark Sudoku isn't one of the puzzle types SudokuStreak generates for now. But you can learn its rules above, and there's plenty here to sink your teeth into meanwhile: