Clusters

You’re given a grid, with several dots inside colored squares. Your objective is to fill every empty space with one of two colors while following these rules:

  1. Tiles which are adjacent to 1 other tile of the same color are denoted with a dot. All of these tiles are given.
  2. All other tiles must be adjacent to 2 or more tiles of the same color.

This puzzle type was invented by Inaba Naoki under the name クラスター, or literally Kurasuta, which Google Translate names ‘Cluster’. The original puzzles are available here: http://www.inabapuzzle.com/honkaku/kura.html

Controls

Left-click to place blue squares. Right-click to place red squares. You can also click and drag to place multiple squares.

To play with a keyboard, use the arrow keys to move the cursor. Press Enter to place a blue square, and press Space to place a red square.

Clusters parameters

These parameters are available from the ‘Custom…’ option on the ‘Type’ menu.

Width, Height
Size of the grid in squares.
Difficulty

Controls how deeply you have to reason. Both settings always have exactly one solution, and neither ever needs a guess.

Easy puzzles can be finished a square at a time: for each empty square, one of the two colors breaks a rule outright, so the other one is forced.

Normal puzzles need at least one step where that is not enough, and you must suppose a color, follow the squares it forces, and find the contradiction further along. Normal boards are guaranteed to need this at least once — a board an Easy player could finish is not offered as Normal.

Normal needs a board with room for the deeper reasoning, so it is not offered on very small grids.

More help