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Nurikabe

A Nurikabe puzzle is played on a grid of cells, some of which have numbers. Another name for this puzzle is "Islands in the Stream" which is a useful analogy when you see the solution.

In a completed puzzle, each cell is either left or marked white as part of an "island", or it is blackened to become part of the stream. The solution must follow these rules:

  • The cells with numbers are by definition white, and part of an island.
  • An island must have as many cells as its number.
  • All the cells in an island must be orthogonally contiguous, i.e. you must be able to get from one cell in an island to any other by some sequence of up/down/left/right moves. (Diagonal moves are not allowed.)
  • Islands cannot touch, except diagonally.
  • Each island must have exactly one numbered cell.
  • All darkened cells must be orthogonally connected to every other darkened cell. (In other words, islands touching diagonally cannot cut off one body of stream cells from another.)
  • One cannot have a 2x2 block of darkened cells.

Puzzle:

Solution:

A Nurikabe is basically a visual logic puzzle. Using logic, the solver decides which of the unnumbered cells must be darkened, and which must be left white. Here are some tips:

  • When you decide a cell must be an island, place a small dot in its center. Shade a cell when you decide it must be a stream cell. At a glance, any cell that is still blank is undecided. If you follow this practice, you will often "see" the only way to expand an incomplete island (or connect an "inlet" of the stream.)
  • Since islands cannot touch orthogonally, any cell that seperates two numbered cells must be stream, so darken it.
  • A cell with the number "1" is a complete island - you can immediately darken the cells above, below and beside it.
  • Once an island is complete, all cells around it can be darkened.
  • If three darkened cells form an L-shape, the fourth cell inside it must be part of an island.
  • All darkened cells must eventually be connected. Often, there is only one "pathway" of undecided cells along which it can connect.
  • All white cells must eventually form part of an island. Often, there is only one numbered island it can connect to, and only one path towards it.
  • At some point, you may need to identify cells that cannot be reached from any numbered cell. These must be darkened.

Occasionally, some trial and error is required. Experienced solvers learn to recognize certain patterns.

Nurikabe is easily printed in black and white and played with a pen or pencil, and is popular with commuters.

Our puzzles are carefully graded by difficulty: Easy, Moderate, Hard and Challenging. All puzzles are rigorously tested to ensure that they have exactly one solution. Various square and non-square sizes are offered; custrom sizes are available.

We provide puzzles and solutions in print-ready format (EPS, or Encapsulated Post-Script) as well as machine-readable format (XML), and can provide custom content and format as required.

Please feel free to download our samples or contact us with your requirements.


DOWNLOAD SAMPLE PUZZLES

Click here to download a zip file with:

  • A PDF document, ready to print, that contains several Nurikabe puzzles of various difficulty levels, with solving instructions, and solutions

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