Hitori is a numerical puzzle created in Japan. Hitori is a 3x3 to 25x25 square field with each cell filled with either a number or a letter. No row or column can have more than one occurrence of any given number. The goal is to find the numbers that have been placed incorrectly and mark them black.
The black cells must to touch either horizontally or vertically, but there can be diagonally adjacent black cells. The cells that remain blank have to touch others, as well as any of the surfaces, and create a single area.
A left mouse click can be used to mark cells black. The cells that duplicate and, therefore, were filled incorrectly are highlighted red. The red color for duplicates in a single row is brighter than the one for duplicates in the same column. The right click can also be used to mark the cells that are most likely not to be black. However, this mark is only supplementary and does not affect the solution check.
To check whether Hitori has been solved correctly, please click the corresponding button. Mistakes are marked in red, whereas the pink color shows the isolated areas. The number of black cells must not exceed the one specified in the problem; otherwise, the check button will become inactive.