Match 3 Game algorithm Part 4 - How to enable the user interaction?

Until now, we manage to come out with a fundamental match 3 game with the matches detection and a deadlock detection. So far so good :)

But the thing is, something is still missing: user interaction. This is the crucial part that lets the players get hooked on the game. The players are required to make some moves to proceed with the games, either through forming more matches, or completing some special missions. (In the case of the candy crush, the missions are forming matches to clear the jelly, or achieving a threshold score with minimum moves, and etc)

Here, the basic user interaction tutorial would be: move the nodes/items, either horizontally or vertically.

At first sight, this is pretty straightforward. In fact, since the each node/item in my match 3 game is coupled with an integer index, it isn't hard to make a rule such that, if the first node touched is a neighbor of the second, both the nodes are exchangeable, and hence we could perform some matching detection algorithm.

For example, the picture shows a matrix of 8x8. At the nodes indexed at 10^th, 17^th, 18^th, 19^th and 26^th, it is easily observed that, the node of 18^th can be only exchanged with its neighbor which has the absolute index difference of 1 or 8. With this understanding, we could conveniently generalize the algorithm...

However, let's consider 1 more case:

Here, the node indexed 15^th, despite being able to exchange with the node 7^th, 14^th, 23^rd, it is unable to interact with the node 16^th (because they are not directly connected). Therefore, this special case has to be addressed in our algorithm, which is stated in the next statement:

Statement 4:
- Two nodes are exchangeable, provided that their absolute index difference is 1 or 8, AND if one of them is in the column 0^th or 7^th, the other one is NOT in the column 7^th or 0^th.

Forgive my poor explanation in the last part. It simply means that, the node in the column 0^th cannot be exchanged with the one in the column 7^th.

Coming up next: Miscellaneous (Special Combinations)