This is a classic 8 queen puzzle. The aim is to place 8 queens on a chess board without threatening each other! Simply tap on a square to place the queen and tap again to remove her!
There are 92 solutions! So you can arrive at a solution by sheer trial and error or you can be smart about it. To make things interesting, the application will place the first queen for you which is immovable. To go a step ahead, you can choose your level of expertise!
Considered as a simple example of an algorithm, it can also be taken up as a challenge for some strategic planning!