How ThinkyPlay Generates Fair Puzzles

The two-step rule that never changes

Every generator works the same way at its core:

• Create a valid completed board (a solution).
• Remove clues — then run a constraint solver that counts how many solutions remain.
• Only publish puzzles where the count is exactly one.

If removing a clue allows a second solution, the generator keeps the clue. The result is a puzzle you can always solve with pure logic.

Per-puzzle solvers

Each game has a solver matched to its rules, not a generic guesser:

• Sudoku & 6×6/16×16: classic MRV backtracking over candidates, checking rows, columns and boxes.
• Nonogram: a line-based solver enumerates whole-row placements instead of guessing cell by cell, which keeps uniqueness checks milliseconds-fast.
• Logic Grid: a CSP propagates values across categories with MRV backtracking, so clues can never contradict themselves.
• Kakuro / KenKen / Killer Sudoku: cage-aware solvers respect run sums and cage operations while pruning candidate domains.
• Skyscrapers / Futoshiki: row-permutation candidates are filtered by the clues before backtracking ever starts.
• Hashi: bridge networks must reach every island with the right degree, forming one connected whole with no crossings.
• Slitherlink: edges are propagated so every vertex ends with degree 0 or 2 and the final loop is a single ring.
• Fillomino / Nurikabe / Star Battle: region and connectivity rules are enforced inside the solver, not checked only at the end.

Generated live vs. curated pools

Two publishing strategies keep wait times instant:

• Runtime generation for puzzles whose uniqueness check is fast — most Easy and Medium boards (e.g. Nonogram up to 10×10, Skyscrapers 4×4 and 5×5, KenKen 4×4) are made in your browser in milliseconds.
• Offline curated pools for Hard boards where proving uniqueness can take seconds — Kakuro, Nonogram 12×12, Skyscrapers 6×6, Futoshiki, KenKen 9×9, Slitherlink and Fillomino Hard puzzles come from pre-generated libraries that were each verified to have exactly one solution before shipping.

What this means for you

• No guessing required — a Hint always points at a logical next step, because logic alone can finish the puzzle.
• No unwinnable daily boards — the Daily puzzle uses the same uniqueness guarantee as everything else.
• Honest difficulty — Hard really means "fewer clues plus a solver that had to work harder", not "more guessing".