How the library puzzles are made

First, a complete grid

The generator tries rows in a seeded random order, keeping equal shares of cats and dogs and rejecting any three matching neighbours across or down. The seed makes the process reproducible. Identical rows or columns are allowed: there are exactly two rules.

Remove tiles while logic still finishes

Tiles are considered for removal one at a time in a random order. A removal stays only when the deductions allowed for the target difficulty can still finish the board.

• Difficulty 1: Pair ends and Middle tile.
• Difficulty 2: also Full share.
• Difficulty 3: also Last spare.
• Difficulties 4 and 5: all five, including Shared finish.

Check the solution and record the steps

The allowed deductions alone finish every board, so no guessing is needed. A separate exhaustive search confirms exactly one solution. The walkthrough records each tile, its animal, the deduction and the tiles that explain it, beginning from the starting animals.

A puzzle is rated from 1 to 5 by its hardest deduction and how often it needs the hardest deductions. The library displays Gentle, Easy, Medium, Tricky and Tough alongside those numbers.

Keep the library boards distinct

The puzzles in this library never start from or end on a copy of a daily, a Journey level, one of the app's tutorial or intro boards, the home page's practice puzzle or another library puzzle, even rotated, mirrored or with cats and dogs swapped. A board that repeats one of those, or misses its target difficulty, is thrown away and a new grid is tried.

Follow a board from start to finish

Choose a size and open a numbered puzzle to play. Its separate walkthrough begins with the same starting animals; the full list of steps and the solution remain readable without scripts. Progress lives only in the open page.