What is minimax algorithm
Rating:
6,7/10
1096
reviews

Thus, when we start the problem, all minimax sees is the start node: It begins like a depth first search, generating the first child. For min nodes, we want to visit the worst child first from our perspective, not the opponent's. Looking at a Brief Example To apply this, let's take an example from near the end of a game, where it is my turn. O choses the move in state 5 and then immediately loses when X wins in state 9. In game theory, and more precisely the theory of zero-sum games, the minimax theorem shows that the minimax solution of a zero-sum game is the same as the Nash-equilibrium. Now, you are ready to write the MiniMax algorithm method.

On the other hand the depth limited version was able to finish fairly quickly. A relatively simple example of this is shown below: Fig. In order to make the game unbeatable, it was necessary to create an algorithm that could calculate all the possible moves available for the computer player and use some metric to determine the best possible move. And that's the minimax algorithm! So we create a tree structure. The nodes which represent the end of the game are terminal nodes of the tree.

To curb this situation, there are a few optimizations that can be added to the algorithm. Similarly, for the third child node also. Making pruning effective How effective is alpha-beta pruning? Either one player will win or a draw will happen. It is used in games such as tic-tac-toe, go, chess, isola, checkers, and many other two-player games. I hope this post will help some of you to appreciate the elegance of this algorithm. So, X will always try to maximize the score and will always choose that move which will fetch X the maximum score. It is only for games where an intelligent player is guaranteed victory by going first or second such as Nim, in many forms that minimax will prove sufficient.

Continuing in this manner the last move will have N D child nodes. It will vary from game to game of course. If you want to write a program that is able to play a strategy game, there are good chances that you will be looking at a Minimax algorithm. Similarly, the lesser the score, the better it is for O, so O will try to minimize the score as much as possible. We want to get the highest possible value here. For this scenario let us consider X as the maximizer and O as the minimizer. Meanings of Alpha and Beta Alpha Best value for us found so far in the current path Beta Best value for opponent found so far in the current path If we find a node with a better value than alpha, we pass this up the tree.

A rook endgame can end in visiting the same board state many times. The algorithm is simple to implement. The condition to prune a node is when alpha becomes greater than or equal to beta. It is sometimes also called Heuristic Function. Also, you may have noticed that the algorithm, as written, requires a lot of memory.

Example So far we know we have to construct a tree structure. It is based on the concept. And that is why we have a computer execute this algorithm. Else it is a min node i. The question now is do we really need to calculate c? We can verify that it works as intended by checking what it does on the example tree above.

It is fun to use Minimax to solve simple games. My question is why I have to write code for both Minimum and Maximum player to return the best move? That move needs to be played. The other way is to grade different positions of tic tac toe board and sum them up. This is done programmatically bu choosing the move which will return the maximum score. So now you've seen the whole search tree.

Summary A future part of this article is pretty much guaranteed as I still have quite a way to go on my quest for writing a semi-advanced game playing program. It does so by exploring only one branch and selecting the candidate value. What is a gosh-darn, tic tac toe master to do? It's perfect play for deterministic games. Since this Game State allows X to win, X should try to get it if possible. Examples of such games are chess, poker, checkers, tic-tac-toe.