I was first shown this puzzle by a friend who found it in a magazine for IBM PC hobbyists. That was when the IBM PC was brand new. The magazine published the Basic source code for this puzzle. My friend had typed the code into his Commodore 64 and asked me to help him get it running. I thought it was a clever little puzzle, so I present it here for your enjoyment. I have added a feature to the original puzzle which allows you to change the rules of the game to make it easier or harder. I allow you to change the rules while solving the puzzle, but that is cheating, so be warned! It is only “fair” to change the rules before starting a new puzzle.
If you have studied linear algebra you might be interested to know that you can treat this puzzle as a linear algebra problem, and that is in fact how my program generates the hints.
To begin working a puzzle, click on the 4x4 grid below and a random pattern of blue tiles will be generated. The object of the puzzle is to remove all the blue tiles from the grid. Blue tiles are added and removed by clicking on the cells of the grid. Which cell you click determines how many and which cells are changed. Rather than try to explain how it works, you can experiment by scrolling down and placing your cursor over the cells of the grid. As the cursor is positioned over a cell, a pattern of cells will be shaded. The shaded cells are the ones that would be changed if you clicked on the cell you are currently pointing to while working a puzzle. A cell is changed by removing the blue tile it contains or adding a tile if it is empty. The only difference between the easy and hard setting is how may cells are changed by clicking on the corner cells. Be sure to click the easy button and observe the difference it makes.
Good luck!