NOTE-KU — how it actually works
There is no difficulty level at which the notation approach breaks down. A harder puzzle simply requires more iteration passes, not a different method.
Most sudoku players solve reactively: scan the board, spot an obvious number, place it, scan again. That works for easy puzzles. Past a certain difficulty, it stops working — the grid resists, the solver stalls, and the experience shifts from satisfying to frustrating.
NOTE-KU is built on a different idea. Notes are not a fallback for when you're stuck — they are the primary tool, used with discipline from the very first empty cell until every cell on the board has exactly one answer.
Select digit 1. For each box on the board, apply the row and column constraints already established by every given number. If exactly one or two cells within that box could still hold the digit, place notes there. If three or more cells remain possible, skip the box entirely and return to it later.
Repeat this for every digit, 1 through 9. By the end of the first full pass, the board holds your first constraint map — incomplete, but already meaningful.
Every new note changes what's possible elsewhere. When a cell has only one candidate remaining, that's a confirmed position — project it across its row, column, and box, and erase that digit from every other candidate note it touches.
Then return to the boxes you skipped. Some now have only one or two candidates left, thanks to the eliminations. Place those notes. Look for the eliminations they enable. Repeat — notation, elimination, notation, elimination — until every empty cell on the board holds exactly one candidate.
When every empty cell holds exactly one candidate, the puzzle is already solved — what remains is confirmation, not analysis. Starting from the last digit that completed the board's notation, fill in every confirmed position in one continuous sweep, moving upward through the digits.
No guessing. No decisions. Every number goes exactly where the notation already proved it belongs.
Why it scales with difficulty
One of the most common questions about the method: does it actually work on expert-level puzzles? Yes — with the same method, applied more deeply. An easy puzzle might need one or two notation passes. An extreme puzzle might need seven or more. The process takes longer, but the method never changes.
| Difficulty | Typical passes | What's required |
|---|---|---|
| Easy | 1–2 | Most cells resolve directly from given constraints |
| Medium | 2–4 | Some elimination required; a few cross-references |
| Hard | 4–7 | Multiple elimination techniques; board-reading skills |
| Extreme | 7+ | Full use of advanced resolution techniques throughout |
In every case: same method, same tools, same final pass. The advanced techniques covered in the NOTE-KU book series aren't replacements for this foundation — they're extensions of it, applied when the basic iteration has been fully exhausted and the board needs to be read at a wider scale.
Play the method free, right now.
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