Ripple Effect: rules, tips and free puzzles online

Ripple Effect is a grid of outlined regions. A region of k cells holds 1 to k once each, and two equal digits in a row or column must have at least that many cells between them. Play Ripple Effect online free here, on grids from 5×5 to 8×8.

In Japan it is called Hakyuu. Each digit sends out a “ripple” as far as its own value, which makes big digits powerful and small ones slippery.

The rules

• The grid is divided into regions. A region with k cells contains each digit from 1 to k exactly once.
• If two cells in the same row or column hold the same digit d, there must be at least d cells between them. Two 1s can’t touch; two 3s need three cells between them.
• Digits already in the grid are given clues.

How to start

Every digit casts a ripple

A placed d rules out d from the next d cells in all four directions, across region borders.

Small regions first

A one-cell region is 1, and a two-cell region is 1 and 2. Combine them with the ripples from nearby digits and many cells resolve straight away.

Where can the big digit go?

A region of five needs a 5, which ripples five cells in every direction. If every place a region could put its 5 is within reach of the same outside cell, that cell can’t be 5. Within a region, pairs work as in sudoku; see our solving techniques guide.

Common mistakes

• Counting the distance wrongly. Two 2s need two cells between them, so they are three steps apart at the closest.
• Applying the ripple diagonally. It only runs along rows and columns.
• Stopping the ripple at a region border. It crosses borders freely.

How the ranks scale difficulty

The same four ranks apply here as everywhere on the site. Lemma is a gentle warm-up, Proposition needs a real idea or two, Theorem is near-minimal with almost every clue load-bearing, and Conjecture is the sparsest of all, so expect to think hard.

Grids run from 5×5 at Lemma to 8×8 at Conjecture, with fewer given digits at each rank. Regions are up to five cells.

There are 99,999 puzzles per rank, each with its own number, so you can replay one or share it. Every type also has a 30-puzzle collection that climbs from Lemma to Conjecture. Every puzzle is checked to have exactly one solution that you can reach by logic alone, with no guessing.

Keep exploring

• SuguruRegions hold 1 up to their size, and equal digits never touch, not even diagonally.
• FutoshikiA Latin square with < and > signs between neighbouring cells.
• KakuroA numerical crossword: runs of distinct digits 1–9 that hit their sums.
• Solving techniquesSingles, pairs, cage arithmetic, line logic and Latin squares, all in one guide.
• All puzzle guidesEvery puzzle type on Hoot’s Puzzles, with rules and tips.