Artificial Intelligence for card battle based game

Question

I want to make a game card battle based game. In this cards have specific attributes which can increase player's hp/attack/defense or attack an enemy to reduce his hp/attack/defense

I am trying to make an AI for this game. AI has to predict which card it will select on the basis of current situations like AI's hp/attack/defense and Enemy's hp/attack/defense. Since AI cannot see enemy's card hence it cannot predict future moves.

I searched few techniques of AI like minmax but I think minmax will not be suitable since AI cannot predict any future moves.

I am searching for a technique which is very flexible so that i can add a large variety of cards later.

Can you please suggest a technique for such game. Thanks

Answer 1

This isn't an ActionScript 3 topic per se but I do think it's rather interesting.

First I'd suggest picking up Yu-Gi-Oh's Stardust Accelerator World Championship 2009 for the Nintendo DS or a comparable game.

The game has a fairly advanced computer AI system that not only deals with expected advantage or disadvantage in terms of hit points but also card advantage and combos. If you're taking on a challenge like this, I definately recommend you do the required research (plus, when playing video games is research, who can complain?)

My suggestion for building an AI is as follows: As the computer decides its move, create an array of Move objects. Then have it create a new Move object for each possible Move that it can see.

For each move object, calculate how much less HP the opponent will have, how many cards they will still have, how many creatures,etc.

Have the computer decide what's most important (more damage, more card advantage) and have it play that move.

More sophisticated AI's will also think several turns in advance and perhaps "see" moves that others do not.

Answer 2

I suggest you look at this game of Reversi I built a few weeks back for fun in Flash. This has a very basic AI implemented, but the basics could be applied to your situation.

Basically, the way that game works is after each move (player or CPU, so I can determine if the player made the right move in comparison to what the CPU would have made), I create a Vector of each possible legal move. I then decide which move provides the highest score change, and set that as best move. However, I also check to see if the move would result in the other player having access to a corner (if you've never played, the player who grabs the corners generally wins). If it does, I tell the CPU to avoid that move and check the second best move and so on. The end result is a CPU who can actually put up a fight.

Keep in mind that this is just a single afternoon of work (for the entire game, from the crappy GUI to the functionality to the AI) so it is very basic and I could do things like run future possible moves through the check sequence as well. Fun fact, though, my moves (which I based the AI on obviously) are the ones the CPU would make nearly 80% of the time. The only time that does not hold true is when I play the game like you would Chess, where your move is made solely to position a move four turns down the line

For your game, you have a ton of variables to consider and not a single point scale as I had. I would suggest listing out each thing and applying a point value to each thing so you can apply importance values to each one. I did something similar for a caching system that automatically determines what is the most important file to keep based on age, usage, size, etc. You then look at each card in the CPU's hand, calculate what each card's value is and play that card (assuming it is legal to do so, of course).

Once you figure that out, you can look into things like what each move could do in the next turn (i.e. "damage" values for each move). And once that is done, you could add functionality to it that would let the CPU make strategic moves that would allow them to use a more powerful card or perform a "finishing" move or however it works in the end.

Again, though, keep it to a simple point based system and keep going from there. You need something you can physically compare, so sticking to a point based system makes that simple.

I apologize for the length of this answer, but I hope it helps in some way.