Games & strategy · course 8 of 105

Sudoku Without Guessing

Solve Sudoku by logic instead of guessing: list a cell’s candidates, then spot naked and hidden singles, naked pairs and locked candidates, the first techniques solvers learn.

4 modules

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What it teaches

The first techniques for solving Sudoku without guessing: listing a cell’s candidates (row, column and box), naked singles, hidden singles in a box, row or column, naked pairs, and locked candidates. The AI asks 3 questions, places you, shows a short card per module, then gives you one grid and one question at a time.

Not for advanced techniques (X-wing, chains) yet.

How long

40 items. About 20-30 rounds for a confident player up to about 45-60 for a beginner, plus a 12-item final: 2 sessions (estimate, not timed with a real student). The tutor gives a one-line save code at the end of each session.

The modules

4 modules, drilled one item at a time.

M0
The basics
Rules and words
M1
Candidates and naked singles
Candidates and naked singles
M2
Hidden singles
Where a hidden single goes
M3
Naked pairs and locked candidates
What a naked pair or locked candidate removes

Before it teaches, it asks

1
How do you play now (paper, an app, which difficulty), and where do you get stuck?
2
List every candidate for r1c1.
3
Where must the 7 go in box 2?

What’s exact, and what isn’t

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Straight from the course’s own notes.

Made and checked by script: Every grid was generated for this course and has exactly one solution; every key comes from the solver’s candidates, and each one is checked against that solution (a single’s digit is the solution’s digit; no removal deletes the solution’s digit). Hidden-single items use cells that have other candidates, so they can’t be solved as naked singles. My one hand-written candidate list matched; the rest are the engine’s output, checked against each puzzle’s solution; a planted-error test was caught.
Sourced: The rule and the technique definitions from Wikipedia’s “Sudoku” and “Glossary of Sudoku”; 7 short quotes matched word for word on the live pages 2026-10-11.
Honest limits: Text grids in a chat (no pencil marks or highlighting); M3 gives the candidate lists in the question so you can focus on the technique.
Not in it yet: Hidden pairs, X-wing and other advanced techniques, full puzzles start to finish, variants.