Hitori Rules: How to Play (With a Printable Example)

The Hitori rules are short enough to learn in a minute: you shade some of the squares in a grid of numbers until three conditions are true. What takes practice is seeing which squares to shade. This page states the three rules exactly, checks them one by one on a real grid made by the LogikLand generator, and lists the mistakes beginners make most often.

What Hitori is

Hitori is a puzzle of logic played on a square grid. Every square holds a number from 1 to the size of the grid. At the start, no square is shaded. Your job is to shade the right squares so that every number is unique in every row and every column among the squares left white. The extra copies of a number are the squares you remove.

The three rules

1. No repeated number among the white squares. In any row or column, a number may appear several times in the grid, but only once among the squares you leave white. The shaded copies do not count.
2. Shaded squares never touch along a side. Two shaded squares may share a corner, but not an edge. So a shaded square always has white squares above, below, left and right of it (or the border of the grid).
3. All white squares stay connected. You must be able to walk from any white square to any other one, moving up, down, left or right through white squares only. A shaded wall that closes off a white square, or a group of white squares, breaks this rule.

That is all. There is nothing to add up, and in LogikLand books every grid has a single solution that can be found by logic alone.

A solved example

Here is an easy 5 x 5 grid on the left and its solution on the right, where the shaded squares are dark grey.

Let us check the three rules on this solution. Rows are counted from the top, columns from the left.

• Rule 1. The fourth row reads 1, 5, 4, 3, 3. The number 3 appears twice, so one of the two 3s is shaded: the fourth square. The white squares of that row hold 1, 5, 4 and 3, each only once.
• Rule 2. Seven squares are shaded. The shaded square in the first row, fourth column and the one in the second row, third column touch only at a corner. The same is true of the shaded square in the third row, fifth column and the one in the fourth row, fourth column. No two shaded squares share an edge.
• Rule 3. The eighteen white squares form one single region. If you start from any white square and move through white squares, you reach all of them.

Mistakes to avoid

Shading every copy of a number

If a number appears three times in a row, you do not shade all three. You keep exactly one of them white, because the rules say the white squares must show each number once. Shading all copies removes the number completely.

Forgetting the corners

Beginners often think two shaded squares that touch at a corner are forbidden. They are allowed. Only a shared edge is a mistake. The opposite error is more costly: a white square in a corner of the grid with both of its neighbours shaded is cut off from the others, which breaks rule 3.

Checking only the rows

The columns follow the same rule as the rows. After each shaded square, check its column as well as its row.

Guessing

A guess that turns out wrong usually forces several more wrong squares before you notice. Our suggestion, not a rule of the puzzle: when you are not sure, mark nothing and look for another square where the rules force an answer. A grid made by LogikLand always has one.

Four sizes

The Hitori assistant makes four levels. The size grows, and so does the amount of reasoning needed.

Making a Hitori book

LogikLand has no free single-puzzle tool for Hitori. The Hitori assistant is reached after you create a free account. In it you choose one level or several, the number of grids per level, 1, 2 or 4 grids per page (2 at most in the 6 x 9 format) and 1, 2, 4 or 6 solutions per page. A "How to play" guide with pictures can be added at the start of the book.

Questions