To play, click on a cell, then enter a digit value. If needed, digit values greater than '9' can be entered by pressing the corresponding letter from 'A' (10) to 'Z' (35). Digit values greater than the largest polyomino ("room") on the board will be ignored. Once on a cell, you can use the arrow keys to move around the board. Press the space bar to remove an entry (except those defined by the puzzle itself).

In Assist Mode (0), the default, only the existance of errors or incomplete rooms is indicated. In Assist Mode (1), the number of errors and incomplete rooms is indicated, see game rules. In Assist Mode (2), errors are highlighted with digit colors, and completed rules are highlighted with tile colors. In some cases the solve difficulty will greatly decrease in Assist Mode (2), so select depending upon the level of challenge desired. The canvas border will turn green if the grid is completed without error. You can click the "undo" button on the bottom of the page to undo previous moves.

Below, enter puzzle code (0-0) for one of a list of pre-defined puzzles, or a puzzle descriptor (see "Puzzles" tab). The following puzzle codes have demos, which will walk you through a solve to help you on the path to mastery: []).

Ripple Effect (波及効果 Hakyuu Kouka) is a Japanese logic puzzle published by Nikoli. In Ripple Effect, the puzzle board is divided a collection of polyominos (or "rooms", i.e. joined sqares) of different sizes and shapes. Each shape contains a number of square tiles, call the number n, where n is at least 1. The rules around these shapes are listed below.

1. For an n-tile polyomino, each of the digits from 1 to n must be represented.
2. In any of the 4 directions (up, down, left, right), there can not be any two numbered digits d within d+1 tiles. For example, there can not be two 3 digits within a 4-tile span. In this way the effects of a number "ripple" out a distance equivalent to the digit's value.
3. All blank cells must be filled in with their appropriate 1-n values so that the above rules are not violated.

Below select puzzle 0 to see a completed sample grid. See the Game Play or Puzzles tab for how to invoke a demo.

Puzzles can be invoked by either a numerical entry from 0-0, or through a character description of the puzzle itself, entered into the Display form on the 'Game Play' tab. The numbered puzzles are hand-crafted of varying difficulty, roughly easy to hard. Puzzle 0 shows a completed correct puzzle.

To describe a puzzle, the character string must be of the form: "WxH:<digit-descriptor>:<wall-descriptor-rows: <wall-descriptor-columns>", where W is a number indicating the width of the grid, and H the height. The digit descriptor is a list of the pre-defined digit contents, from left to right, then top to bottom. Blank cells are represented with a '-' character. To assist in the definition of a sparse board, a combination of b consecutive blanks can be represented with a lowercase letter from 'a' to 'z', corresponding to 1 to 26 consecutive blanks. Digit values greater than '9' should be represented with capital letters 'A' to 'Z' representing 10 to 35. A dot '.' can be used as a visual separator, for example between rows. The wall descriptors are a description of the true/false nature of the walls for each row, and then each column. These are denoted in hexadecimal value, which is a value from 0 to 15 denoted as 0-9,a-f for each collection of 4 walls, ignoring the sides. As an example, if a grid is 8 columns wide, then 7 wall values are needed to define the walls between column 0 and 1, then 1 and 2, etc. These 7 values are described in two-character hex values from 00 to fe. Extra unused bits for the end of a row or column are ignored, and each new row or column begins with a new hex pair or triplet. So if the top row has a wall between columns 0 and 1, and between columns 5 and 6, that would be binary value of 1000010, which is represented as the hex pair of 84. An example descriptor is as follows for entry 1: 'descr'.

For Ripple Effect there are 1 demo puzzles that can be helpful to walk through solving methods. They are puzzle codes []. Enter them in the Game Play tab with the code number and there will be added a demo panel to help with the solve.

This playground was written using javascript and is available open source. All code is checked into the github repo at ohmec/puzzles. Feel free to file bugs there!