Expert Sukaku

A digit-free variant — only pencil marks are given, not final answers. Solve from candidate sets rather than placed digits.

Easy Medium Hard Expert

Expert Sukaku. X-Wings and forcing chains on a fully pre-marked board. Every elimination must be proved, not guessed.

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Mistakes
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Score
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Time
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Tap a number to eliminate it from selected cell
All Sukaku Puzzles →
Progress0%

What is Sukaku?

Difficulty
★★★☆☆
3/5
Constraint Type
Pencilmark Elimination
Typical Givens
All candidates shown
Avg. Solve (Expert)
62 min

Solving Techniques for Expert Level

Technique Description Level
Candidate Scanning Start by scanning rows, columns, and boxes — any candidate appearing in only one cell in a group must be placed there. Beginner
Cross-Hatch Elimination When a digit is placed (or reduced to one candidate), eliminate it from all cells in the same row, column, and box. Beginner
Naked Singles A cell with only one remaining candidate is a naked single — the digit is forced. In Sukaku, this happens automatically when you eliminate down to one candidate. Intermediate
Hidden Singles A candidate that appears exactly once in a row, column, or box must be placed in that cell regardless of how many other candidates that cell shows. Intermediate
Pair Elimination Two cells in a group that share only the same two candidates form a naked pair — both candidates can be eliminated from all other cells in that group. Advanced

Average Solve Time by Difficulty

Easy
8 min
Medium
18 min
Hard
35 min
Expert
62 min
Want a full walkthrough of rules, strategies, and solving steps? How to Play Sukaku →

Frequently Asked Questions — Expert Sukaku

Is expert Sukaku harder than expert regular Sudoku?
Expert Sukaku presents the same logical depth as expert regular Sudoku but with a different surface feel. All candidates are visible from the start, which removes the pencil-mark setup step but makes the board visually dense. The underlying techniques — X-Wings, Swordfish, forcing chains — are identical, but you must track them in a field of preprinted marks rather than your own notes.
What is an X-Wing in Sukaku and when do I use it?
An X-Wing applies when a digit appears as a candidate in exactly two cells in each of two different rows, and both rows share the same two columns. The digit must go into one of the two diagonal pairs, so you can eliminate it from every other cell in those two columns. This removes candidates that no simpler technique can touch.
Can expert Sukaku be solved without guessing?
Yes. Every expert puzzle on Sudoku.by has a unique solution reachable by logic alone. If you feel forced to guess, a constraint you have not yet applied will break the deadlock. Revisit locked candidates, look for hidden pairs, and check whether any X-Wing or Swordfish pattern exists for digits that appear frequently across multiple rows.
What is a Swordfish pattern and does it appear in expert Sukaku?
A Swordfish is a three-row extension of the X-Wing. If a digit appears in exactly two or three candidate cells in each of three rows, and those cells collectively span only three columns, the digit must occupy one cell from each row within those three columns. Every other candidate for that digit in those columns can be eliminated. This pattern appears occasionally in expert Sukaku.
How long does an expert Sukaku take?
Expert Sukaku typically takes 60 to 90 minutes for experienced solvers. The density of candidates on the board demands careful, methodical scanning. If you spend more than 15 minutes without progress, revisit the most constrained rows and columns — there is almost certainly a locked candidate or hidden pair you have overlooked.

More questions? See the full Sukaku guide.