Author: Anurag Sahay
Place the given pentominoes into the grid. Pentominoes may be rotated and reflected. Elements can not touch each other, not even diagonally. All painted cells belong to pentominoes and indicate every third cell used by pentominoes scanning the grid row by row from left to right.
Grid control: Click the mouse button at the selected cell to change the color of the cell. Second click will put auxiliary cross sign, which doesn't affect correctness of the solution, but helps visually. You can also drag the content of one cell to another with the mouse. You can also click on the given tetromino figures to mark them out. More details about grid control are at the help page.