﻿ Nurikabe solving strategy for Islands in the Stream
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# PUZZLE TECHNIQUES

## NURIKABE SOLVING TECHNIQUES

Only solve nurikabe puzzles using logic. Here are some solving techniques:

### ISLAND WITH NUMBER ONE

Because this is an island with one cell the horizontally and vertically adjacent cells may become blue.

### DIAGONALLY ADJACENT NUMBERED CELLS

When two numbered-cells are diagonally adjacent then cells touching both numbered-cell must be blue and become part of the sea.

### NUMBERED CELLS SEPARATED BY ONE CELL

When two numbered-cells are in the same row or column and saparated by one cell, then the cell in between must become a blue cell according to the nurikabe rules saying that each island may only have one numbered cell.

### ISOLATED CELLS

The cell in the right bottom corner is isolated and cannot become part of an island. So therefore that cell can only be part of the sea and becomes blue.

### FORM ONE UNINTERRUPTED SEA

All blue cells, according to the nurikabe rules, must form one uninterrupted sea. By adding 3 blue cells we avoid that the blue cell below number 4 gets separated

### EXPANDING ISLANDS

In the grid below, the island of 4 can only be expanded upwards and the island of 5 can only be expanded to the right. These cells will be marked with a dot to show they are part of an island and cannot be part of the sea.

### EXPANDING ISLANDS IN TWO DIRECTIONS

Sometimes the last cell of an island can only be expanded in two directions. If that is the case, then the cell diagonal to the island must become part of the blue sea.

### AVOIDING 2X2 AREA

Sometimes a cells must be part of an island to avoid an sea area of 2x2.

### COMPLETED ISLANDS

If an island is completed (island 3 example below) we can surround this island with horizontally and vertically adjacent blue cells.

### UNREACHABLE CELLS

If cells are too far away to belong to any island, then they become blue to indicate they must be part of the sea.

### IF CONFLICT THEN OTHER CHOICE

IF the cell with the question mark is part of the sea THEN the two cells with an exclamation must also become blue because they unreachable by a numbered cell. This would create an 2x2 area what is against the rules. So the cell with the question mark becomes a dot-cell and the two cells with an exclamation now may become blue.