Hitori is a puzzle game from the family of Sudoku puzzles.
Each puzzle consists of a square grid of numbers.
The objective is to mark the cells with green or red colors so that no row or column contains a duplicate number.
Click once to mark the cell green and click second time to mark it red. Clicking third time will unmark the cell.
Mark cells red to remove duplicate number and green to keep the number.
Red cells must not touch each other vertically or horizontally while all green cells must create a single continuous area.
More details can be found here