Counting the Sea

Medium Used by Smart Hint

The sea's total size is fixed from the start: the whole board minus the sum of every clue. Once the marked sea reaches that count, every remaining blank is land — and once marked land reaches the clue total, every blank is sea.

Island (land)
Sea
Cells that establish the pattern
Where the conclusion lands

How it works

The sea's size is fixed before the first move: 16 cells minus the clue total of 5 + 1 + 1 = 7 leaves exactly 9 sea cells.
Nine sea cells are already marked — the sea is complete, and no further cell can join it.
Every remaining blank must therefore be land, no matter which island it ends up joining. Here the four of them finish the island of 5.