Ripple Effect Puzzle Generator
Ripple Effect is a number puzzle where a number decides how much room it needs. Each room holds 1 up to however many squares it has, each number once. Then, wherever the same number turns up twice in a row or a column, it must have at least that many squares of clear space between the two: two 1s cannot sit side by side, and a pair of 5s has to stand five squares apart. Big numbers ripple outwards and force small ones into the gaps, which is where the solving happens.
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
- Pick a grid size and how large the rooms should run.
- Fill each room with 1 up to the number of squares in it, using each number once.
- Check every row and column: equal numbers need at least that many squares between them.
- Start with the largest rooms — their big numbers reach furthest and rule out most.
- 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 about five seconds at its worst and under one for a typical grid, and larger grids grow quickly from that.
- Rooms
- How large the rooms are allowed to grow: no room is ever larger than the setting says, so small rooms mean no number above 4 anywhere in the grid. 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 while the generator is unchanged, so a puzzle can be set twice or reprinted. Deterministic, not cryptographic.
Worked examples
- Seed lighthouse on a 6 by 6 grid with mixed rooms
- Ten rooms of two to five squares, and four printed numbers — two 5s, a 1 and a 2 — out of 36 squares. The other thirty-two are left to the two rules.
Common use cases
- A number puzzle that is nothing like a sudoku, for someone who has had enough of those
- A printable page where the same digit may repeat in a row, provided the gap between the two is at least that digit
- 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 is proved to survive. A proof that runs out of its budget keeps the number, so very occasionally one printed number is spare: 1 of 341 in a 72-grid sample, counted by a second solver that shares no code with this one.
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: with rooms held to four squares, none of 20 builds found a legal filling at 7 by 7, and none of 20 at 8 by 8.
- Eight squares a side is the largest grid, where a typical build takes under a second of processor time and the slowest of twenty took about five.
- 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.
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