Puzzle methodology
How Legen generates, verifies, and publishes Sudoku puzzles.
Every published puzzle follows a deterministic path from a candidate grid to a stable Puzzle ID, a unique solution, a verified logic trace, a versioned difficulty score, and a permanent source page.
“Legen Puzzle Engine verified” means the stated givens have exactly one solution and every claimed logical step was accepted by a separate proof verifier for the published engine version. It does not mean a human expert reviewed every puzzle.
1. Puzzles are generated before publication.
Puzzles are prepared and checked before they appear on the site. A puzzle stays fixed at its permanent URL, so reloading the page does not create or change it.
2. Format and uniqueness are checked first.
The engine validates all 81 cells, rejects conflicting givens, and counts solutions with a fixed search budget. Only a puzzle with exactly one solution can enter the published catalog.
3. Every stated logic step is checked again.
Before a placement or candidate elimination is shown, a separate check confirms the target cell, digit, row, column, box, pattern, candidates, and current board state.
4. Difficulty is versioned, not guessed from clue count.
LDI v0 uses the hardest verified technique, weighted logical work, and explicit candidate eliminations. The score is bound to a named engine and LDI version; historical values are not silently rewritten.
5. Only the public puzzle facts are published.
The site publishes the puzzle and the verification facts needed to understand it. Private generation data and unpublished diagnostics are not included in pages or downloads.
6. Corrections stay traceable.
A confirmed factual correction receives a dated note and is checked again. Changes to the engine, scoring formula, data format, or puzzle facts are published under a new version instead of being silently rewritten.
What this method does not claim
- It does not measure intelligence, human completion time, or a universal notion of Sudoku difficulty.
- A complete verified engine path is one valid logical path; another solver may choose a different valid path.
- No completion-time, hint, error, account, region, or other player-behavior data enters LDI v0.
- The downloadable sample is a compact public dataset; it does not include private generation data or unpublished per-puzzle diagnostics.