Zuma is one of my favourite games of Fantasy Games series. In the game a lot of balls of different colors will enter the screen continuous, and the balls onscreen are rolling by a fixed track in a queue. You can control the stone frog located at the center of screen to fire balls. The balls fired can be inserted into the rolling balls queue. When there is a group of 3 or more balls of the same color touching, they explode! You should eliminate all the balls before they reach the skull which lies on the end of the track.

Let's consider a simplified game mode. There is a queue of balls of different colors given. At each time you can fire a ball of arbitrary color into the queue at arbitrary position (either between two balls or at one end of the queue) . Arbitrary means that you can choose the color and the position on your behalf. When there is a group of 3 or more balls of the same color touching, they explode, and you will get a number of points which equals to the square of the length of the group. Explosion causes the balls on either side to slide together, perhaps chain-reacting into another explosion.