How Computers Think About Their Next Move

Have you ever wondered how computers play games like chess or Tic-Tac-Toe? How do they decide which move to make next? The answer involves something called adversarial search, a super cool AI technique that helps computers make smart decisions when playing against an opponent.

What Is Adversarial Search?

Adversarial search is how computers figure out what moves to make in games where:

• There's an opponent trying to defeat you
• Players take turns making moves
• Each player has opposite goals (if you win, they lose)

Unlike regular problem-solving where a computer just finds the best path to a goal, adversarial search must deal with a critical challenge: there's an opponent actively working against you!

Games Are Special Search Problems

When you play a game like Tic-Tac-Toe against a friend, you're not just making random moves. You're thinking ahead: "If I place my X here, what will my opponent do next? And then what will I do after that?"

This is exactly what makes games different from regular problems. In a game:

• There's an opponent who is actively trying to win against you
• The best solution isn't just a sequence of steps but a strategy that accounts for your opponent's moves
• You need to think several moves ahead, anticipating what your opponent might do

Here's a summary of what makes adversarial search different from regular search problems:

Regular Search	Adversarial Search
Find a sequence of actions to reach a goal	Find a strategy that works against an opponent
You control all decisions	You and your opponent take turns
Plan a complete solution from start to finish	Must adapt to opponent's counter-moves
Example: Finding the shortest route on a map	Example: Deciding the next move in Tic-Tac-Toe

Tic-Tac-Toe With Adversarial Search

Tic-Tac-Toe is simple enough that we can actually map out all possible game states! Let's break it down:

• The game board has 9 spots
• Each spot can be a cross (X), a knot (O), or empty
• Players take turns placing their symbol

When playing Tic-Tac-Toe, you're mentally exploring a "game tree" – a structure that shows all possible game states based on different moves by both players.

Let's Meet Max and Min

To understand how computers approach games, imagine two players:

• Max (who places X's) tries to maximize the score
• Min (who places O's) tries to minimize the score

This is why the main algorithm for game-playing is called the Minimax algorithm. It assumes that:

1. Max makes the best possible move for their position
2. Min makes the best possible move for their position
3. Both players think ahead about what the other player will do

In the next part...

We'll see exactly how the Minimax algorithm works by walking through a simple Tic-Tac-Toe example, and understand how computers evaluate different game positions to make the best moves possible!

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Fun Fact: The first computer program to play chess was written in 1950, but it took until 1997 for a computer (IBM's Deep Blue) to defeat chess grandmaster Garry Kasparovthe!