KNS Puzzles offers the Hitori puzzles in the following formats:
5 x 5 - Level 1 - Level 2
6 x 6 - Level 1 - Level 2
7 x 7 - Level 1 - Level 2
8 x 8 - Level 1 - Level 2
9 x 9 - Level 1 - Level 2
12 x 12 - Level 1
Eliminate numbers until there are no duplicates in any row or column. Eliminate numbers by marking them in Black. You are not allowed to have two Black squares touching horizontally or vertically (diagonally is ok). Any White square can be reached from any other (i.e. they are connected). What is the objective? You are to eliminate duplicate numbers in the rows and columns. You can only have (at most) one of any given number in each row and column (sometimes none). Sometimes you don't have any of a given number in a row or column, and sometimes there are no Black squares in a row or column.
This is the start of the puzzle.
As we're only allowed one <3> in Column 4, one of these squares is Black. Whichever that is, the square between the two must be White.
As we've now found a <5> in Column 4, all other <5>'s in the same Row or Column must be Black.
All squares surrounding a Black one must be White.
We've found a <3> in Column 3, so this square is Black (and those surrounding it are White).
This square is Black as we've already a <3> in Column 4.
We are not allowed isolated White squares, so this square must be White to avoid the <5> in the corner becoming isolated.
We've already a <1> in Column 5, so this square is Black
These squares must be White to avoid isolated White squares.
These squares are Black as we've already a <4> in Row 3, and a <3> in Column 2.
This square must be White to avoid the bottom White section becoming isolated.
This square must be White as we've already a <1> in Column 2, and the puzzle will then complete.
The completed puzzle.