Light Read #1 – Inverting the Nurikabe

Nurikabe (or sometimes known as “Islands”) is one of the classic puzzle type made famous by Nikoli. The numbers inside the grid represent an island that many cells wide. Islands, series of white squares, can only touch other islands diagonally. The remaining cells, representing the ocean, are shaded. The ocean has to interconnect throughout the grid and no 2×2 squares can be shaded.

In most Nurikabes, there is more ocean than there are islands; hence, more shading than leaving cells blank. When solving on paper, this gets really annoying for several reasons. Firstly, there are problems with cleanliness, shading in like crazy will imprint unwanted marks and smudges in the next page and the opposite page when you close the book.

Secondly and debatable, you tend to visualize things better if the islands were shaded and oceans left blank. Similar to what you originally do to islands, you can dot the oceans.  When you encounter 3 of 4 shaded cells of a 2×2 square, you tend to dot the remaining cell to represent an island and must somehow weave to that cell, but vice versa, shading in the leftover cell from the 3 of 4 dotted cells is more convenient.

I do this all the time when I’m solving on paper, after a while you get so proficient that dotting isn’t even necessary.

From Nikoli Puzzle Box 9

Does anyone else solve it this way?

Would this notation get me penalized in tournaments?

Here is a Nurikabe from my puzzle shed.

Nurikabe – Shade in black cells, representing the ocean, to isolate several islands (interconnected series of white cells). Islands cannot be adjacent to any other islands. The numbered cell (part of different islands) shows the size of that island. There can be no 2×2 shaded cells of ocean.

(Somewhere Over the Rainbow, Oct 2012)


4 responses

  1. I solve it in what I think is the conventional way used by a lot of solvers, although I do agree with most of your reasoning here. I think its up to the person which to shade and which to leave blank. At least in competitions I have participated, there is no restriction on the type of markings used in a puzzle as long as they are consistent throughout the puzzle, so you definitely won’t get penalized for it.

  2. Both ways have their merits and demerits.Personally i felt the conventional one holds slightly more benefits.When i shaded the islands,i found it a little more useful to play with the constraint that two islands are not orthogonally adjacent,but thats the only good thing i could see with that approach.

  3. I use a variation of your notation – I mark the islands with large (e.g. Hitori) circles (it reminds me that they are ‘white’, and is quicker than full shading), and I dot the water cells, but I also join all the waters together with a single branching line, so that I can quickly see which sections of it are connected.

  4. Pingback: Light Read #2 – Not numbers? No thanks! | Somewhere Over the Rainbow

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