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)