The Doppit Almanac · No. 09

Islandit, a daily Nurikabe

Flood one sea around numbered islands

What it is

Islandit is Doppit's Nurikabe, the Japanese puzzle of flood and stone. The board opens dry, salted with numbers. Each number seats an island of exactly that many cells, you flood everything else, and whatever the sea does not swallow is land.

The pleasure is in the negative space: you paint only the water. Every deduction starts with counting, since a 2 reaches one cell past its clue and any square beyond every number's reach is already sea. Mistakes glow as you make them, and finished islands turn green. The craft, all the way down, is knowing where the sea cannot go.

How it plays

The maritime law is short.

• Every number anchors an island of exactly its size, and an island holds exactly one number.
• Islands never touch side by side. Corners are fine.
• The sea is one connected body of water.
• No 2×2 patch of cells is ever all sea. Square ponds are forbidden.
• Land marks are notes. Blanks already count as land, so an island sealed in water is settled.

The difficulties

Three tides are posted daily. Easy ebbs away in thirty seconds to a minute. Medium takes one to three minutes of careful coastline. Hard is three to six minutes and saves one narrow strait for last. Expert is a thirteen-by-thirteen board, and eight times over, you must suppose a square wrong and follow it four cells further before a rule breaks. Expert never comes round as a daily; it is yours to practise on. A new board floods in every day, and it costs nothing.

Nearby in the almanac: Yinit, Aquait and Campit