Ripple Effect Puzzle Generator

What this generator does

Grows rooms across the grid, fills them so every room and the spacing rule are satisfied, then takes printed numbers away one at a time — keeping a removal only while the numbers that remain still lead to a single filling.

How to use this tool

1. Pick a grid size and how large the rooms should run.
2. Fill each room with 1 up to the number of squares in it, using each number once.
3. Check every row and column: equal numbers need at least that many squares between them.
4. Start with the largest rooms — their big numbers reach furthest and rule out most.
5. Show the answer when you want to check the grid you have filled.

Understanding the controls

Grid

Five to eight squares a side. Eight is the largest offered because the whole build is measured there at two seconds at its worst, and larger grids grow quickly from that.

Rooms

How large the rooms are allowed to grow. Small rooms are offered up to six squares a side only: on a larger grid they make so many 1s and 2s that the spacing rule leaves no legal filling at all, which was measured rather than guessed.

Seed (optional)

Any word rebuilds the same grid later, so a puzzle can be set twice or reprinted. Deterministic, not cryptographic.

Common use cases

• A number puzzle that is nothing like a sudoku, for someone who has had enough of those
• A printable page for a puzzle club, a newsletter or a waiting room
• Practice at reasoning about distance rather than about rows and columns
• Setting the same grid for several people by sharing the seed
• A short puzzle at five squares a side, or a long one at eight

How this generator works

The answer grid is drawn by the same routine that later proves the puzzle, with the numbers it tries shuffled — so the answer is legal by exactly the definition the proof uses rather than by a second, looser one. Solving narrows each empty square to the numbers its room and the spacing rule still allow and fills the tightest square first, which finds a dead branch early instead of at the far end of it. Printed numbers are then taken away one at a time, each removal kept only while a single filling survives, so every number left on the page is doing work.

Randomness and fairness

The rooms and the filling both come from your browser's cryptographic random source unless you type a seed. A seed is for reproducibility, not cryptographic strength — it makes the identical grid come back, and anyone with the seed can rebuild it.

For how randomness is produced across the whole site, see how Generate Random works.

Limitations and good to know

• Small rooms are refused above six squares a side. That is a shortage of puzzles rather than a slow build: at 7 by 7, 16 of 20 attempts found no legal filling at all, and at 8 by 8 none of 20 did.
• Eight squares a side is the largest grid, where the slowest of twenty builds took about two seconds of processor time.
• Difficulty is not graded, and because every removable number is removed, the grids tend towards the demanding end.
• Rooms are grown at random rather than designed, so a grid will not have the symmetry a hand-made puzzle often does.
• Rooms are outlined with the heavy lines a screen can draw; there is no separate layout tuned for a printer.

Privacy and your data

Rooms, filling and proof all happen in your browser. Nothing you type as a seed, and no puzzle or answer built from it, leaves the device.