SCORE:

## How to play

Hitori is a game played on a rectangular grid of numbers. The aim is to eliminate cells (by turning them black), so that the following rules are followed,
1. Each row and column may only contain each number once (i.e. in white). Note that this does not mean that a row or column has to contain any particular number.
2. You can't have two black cells next to each other. Linked diagonally is fine.
3. All the white squares must be one single connected whole, i.e. from any white starting square, you must be able to reach any other white square by only moving to adjacent white squares. Diagonal moves are not allowed.
From these rules we can make a few conclusions,
• If you decide a particular square is black, then all the squares next to it must be white (see rule 2).
• If you have decided a particular square is white, then all other squares in the same row/column with the same number must be black.
• If turning a cell black would create two separate areas of white cells, then that cell must be white.
• In a sequence of three squares with the same number, the one in the middle must be white, to avoid having two black numbers next to each other.
• Similarly, if you have a square between two identical squares, then your original square must be white, as one of the two identical squares must be black.
• If a row contains two identical squares next to each other, then all other squares in that row with the same number must be black. One of the two identical squares must be white, so any other squares in the same row with the same number must be black.
• If you have a set of 2*2 squares with all the same numbers, then two of them must be black, and they must be diagonal from each other. Similarly, two of them must be white. There's only two possibilities for this, it is often worth looking to see if one of the possibilities would cut off another white section of the grid. If this set of 2*2 squares is in the corner, then the square in the corner must be black, otherwise you're going to cut off a white square from the rest of the grid.
This is an example of a completed Hitori puzzle. Note that the each row and column has only one of each number in white, there aren't any black cells touching another black cell, and all the white cells are one single connected whole.
This is an example of a starting grid. I have highlighted two cells that we can start with.
• Look at the left-most column. There are two 7s together at the bottom, since we can't have remove both of these cells, one must be black, the other must be white. We don't know exactly which way round (yet). Since we can only have one white number in each column, the highlighted 7 must be eliminated.
• We can apply the same technique to the highlighted 6, but by looking at the row instead.
We can also go a step further, since eliminated black cells can't touch any other eliminated black cells, then all the cells around the 7 and the 6 must be white.
We now have 7 cells in white. For each of these we can now look at each in turn, and eliminate any duplicates from the row/column.
That gives us this grid. We now apply the same process again, all the cells surrounding any black cells must be white.
This is where rule 3 starts to come in to play. The white cells must be one single connected whole. We have a 4 in the top-left with a 2 just to the right of it. This 2 must be white, otherwise the 4 would be isolated and we would have created two islands of white cells.
We can apply this same reasoning to the white 2 in the left-most column, the 7 next to it must also be white.
We can now apply these same rules to finish this puzzle.
This page will automatically load the puzzle for today. If you want to play a different puzzle, go to the archive page and choose your puzzle.
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.

### Playing with a mouse/touchscreen.

• When you have found a square where you can enter a number, click/touch that square. The square will turn light black.
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 black. Click/touch the pencil icon above or below the puzzle. This icon will turn light black, 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 black. 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.

### Playing with a mouse and keyboard.

• You will need to select a square by clicking on it with the mouse, it will turn light black. 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.
Any mistakes you make will be hilighted in red. The website will know when you have completed a puzzle and will tell you. If you have an account and are logged in, the website will remember that you have completed that puzzle. You will also take part in out leaderboards. It's free to create an account!