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The rules to Nurikabe are actually quite simple, but they combine together to give some wonderful logic problems.
The challenge is to construct a maze (where the white squares are the walls), that satisfy these rules,

- The walls are made of connected adjacent stone blocks.
- The squares with numbers in them are part of a wall. That particular wall must contain exactly that number of squares, e.g. A square with the number 4 in it means that it forms a wall with 3 other squares.
- Walls may not touch each other, even if they have the same number (diagonally is fine).
- All the squares that are not part of the wall make up the maze.
- The maze must be one single connected whole, i.e. from any blue starting square, you must be able to reach any other blue square by only moving to adjacent black squares. Diagonal moves are not allowed.
- The maze can't contain any 2x2 'rooms'

From this set of rules, we can make a few deductions,

- Once a wall has it's correct number of squares, all the squares around that wall must be blue.
- As a special case of the first rule, if we see the number '1' in a square, then all the squares next to that square must be blue. This is usually how we start a Nurikabe puzzle.
- If we see two squares with numbers diagonally from each other as in this example:

then for those two walls to be seperated, the other two squares in this example must be blue. - If we see three blue squares forming an 'elbow' like this,

then we know the other square in this image must be white to avoid breaking rule 6. - All blue squares must be connected, so if there is an undecided square(s), and if the only way to connect two seperate areas of blue squares is for the undecided square to blue, then that square must be blue.
- All white squares eventually belong to a wall. So if we have an isolated white square, and there is only way for it to connect to a wall, then those squares must be white.
- You will sometimes find some undecided squares that cannot be reached from any island, or in doing so would break another rule, then in that case, that square must be blue.

This is an example of a completed Nurikabe puzzle. You will see that the blue area is one completely
connected whole. Each of the white walls contains the correct number of blocks, and that none of them are
connected.

This is an example of a starting Nurikabe grid. Every puzzle will contain a limited number of walls that are
only one block in size. The first thing we will do is surround those 1-block walls with blue blocks.

In this puzzle we also have two walls that are only separated diagonally (the two that have a '5' in
them), so we will place blue blocks between them to separate them.

We can now decide on those cells with a red cross in them. If the highlighted square in the top left was a
wall, then it would block off the blue block above it, which would be against the rule 5. So, this cell
must be blue.

Looking at the two cells in the bottom left, they also can't be walls as there isn't a wall starting block
that can reach them. If a particular cell is to be a wall, then it must be close enough to a wall starting
cell that it can be reached. The '2' between the two highlighted cell can't reach either of the highlighted cells.

We can now decide on all of the highlighted cells.

- The wall with 4 blocks must expand in to the highlighted cells as there is nowhere else for it to expand in to. We can also surround this wall with blue blocks.
- The cell on the left handside must be blue, as there isn't a wall that can reach it. The wall with 7 cells is long enough to reach it, but in doing so it wouldn't give the '3' enough space to expand in to.
- The cell at the bottom must be a wall, otherwise you would have a 2x2 block of blue cells, which is against rule 6.
- The remaining highlighted cell on the right must be blue, as there is no wall that can reach it.

We have made great progress in solving this puzzle. The rest of the puzzle can be solved using the same
techniques.

The single white cell has been highlighted as a mistake as it isn't currently connected to any other wall -
this will be removed once it is connected to another wall.

There are two ways to play a Sudoku puzzle, you can just use the mouse/touchscreen, or you can use the mouse and keyboard. You can switch between the two methods any time you like, and can use a combination of both.

- When you have found a square where you can enter a number, click/touch that square. The square will turn light blue.

Above and below the puzzle is the number selection. Click/touch the number you want to enter in to that cell. If there is already a number in that square, it will be over-written. - If you want to enter a pencil mark, click/touch the square you want to put in a pencil mark. It will turn light blue.
Click/touch the pencil icon above or below the puzzle. This icon will turn light blue, and you are now in pencil marks mode.

Whenever you click/touch a number now, a pencil mark will be put in the square instead. To remove a number as a pencil mark, make sure you are in pencil marks mode, and click/touch the number again.

You can exit pencil mark mode by clicking/touching the pencil icon, it will turn back to normal. - If you want to clear a particular square, make sure that square is selected and is in light blue. Click/touch the eraser icon. If there is a number in that square, it will be removed. If you click/touch it again, any pencil marks in that square will be removed.

- You will need to select a square by clicking on it with the mouse, it will turn light blue. You can change the current square by using the cursor keys on your keyboard.
- To enter a number, press that number on the keyboard. If there is already a number in that square, it will be overwritten. To remove a number, press the backspace or delete key on your keyboard.
- To enter a pencil mark, press control, shift, or alt on your keyboard at the same time as pressing a number key. Do the same thing again to remove that pencil mark.

Nonograms

Wordsearch

Nurikabe

Jigsaw Sudoku

Samurai Sudoku

Sudoku

Mathdoku

16 × 16

Giant Sudoku

Hitori

X-Sudoku

Kids Sudoku

12 × 12

Giant Sudoku

Hyper Sudoku

Futoshiki

Towers

Killer Sudoku

Greater Than

Sudoku

Maze

Arrow Sudoku

Center Dot Sudoku

Consecutive Sudoku

Odd Even Sudoku

SudokuXV

Network

Minesweeper

Hashi

SlitherLink

TicTacToe

Cell Blocks

Suguru

Kakuro

Train Tracks

Battleships