# Lecture 19:Introduction to Game playing|Minimax Algorithm

TLDRThis video introduces game playing in artificial intelligence, focusing on symbol game strategies. It explains the concept of a game involving players, rules, moves, and payoffs. The video discusses the minimax algorithm, a recursive backtracking algorithm used for decision-making in game theory. It highlights the algorithm's role in game trees, where it aims to compute optimal moves for players, alternating between a maximizing player and a minimizing player. The script also touches on the challenges of the minimax algorithm, such as its exponential growth in complexity, and hints at the solution provided by alpha-beta pruning, which will be detailed in a subsequent video.

### Takeaways

- 😀 Game playing is an important application of artificial intelligence, often involving complex strategies.
- 🎲 A game in AI consists of players, rules, moves, and a set of outcomes or payoffs, which are quantified as utility.
- 🔍 Artificial intelligence uses searching techniques like depth-first search for game playing, as opposed to breadth-first search due to high branching factors.
- 🌳 The minimax algorithm is a recursive or backtracking algorithm used for decision-making in game theory and AI.
- 🤔 Minimax involves two players, 'max' and 'min', where 'max' aims to maximize the score and 'min' tries to minimize it.
- 📈 The algorithm constructs game trees, which are applicable for small games, and uses depth-first search to evaluate moves.
- 🏁 Terminal nodes in the game tree have predefined values that contribute to the decision-making process.
- 📊 Minimax computes the optimal move for each player by evaluating the game tree from the root to the leaves.
- 🚧 A significant challenge with the minimax algorithm is its exponential growth, which can lead to inefficiency in large game trees.
- ✂️ Alpha-beta pruning is introduced as a technique to overcome the inefficiency of the minimax algorithm by reducing the number of nodes evaluated.

### Q & A

### What is the primary focus of the video lecture?

-The primary focus of the video lecture is on game playing in artificial intelligence, specifically discussing symbol game strategies and the minimax algorithm.

### What is considered a game in the context of artificial intelligence?

-In the context of artificial intelligence, a game is defined as a set of two or more players, a set of rules, a set of moves for each player, and a specification of payoff or outcomes for each combination of strategies.

### Why are complex games not discussed in this video?

-Complex games are not discussed in this video because the focus is on symbol game strategies, which are more applicable to smaller games where game tree construction is feasible.

### What are the two searching techniques used in game playing?

-The two searching techniques used in game playing are the minimax algorithm and alpha-beta pruning.

### Why is depth-first search preferred over breadth-first search in game playing?

-Depth-first search is preferred over breadth-first search in game playing because the branching factor in complex games can be very high, making breadth-first search time-consuming.

### What are the two players in the minimax algorithm?

-The two players in the minimax algorithm are 'max' and 'min', where 'max' tries to maximize the score and 'min' tries to minimize the score of 'max'.

### How does the minimax algorithm use depth-first strategy?

-The minimax algorithm uses depth-first strategy by recursively exploring as far as possible along each branch before backtracking.

### What is the main problem with the minimax algorithm?

-The main problem with the minimax algorithm is that it grows exponentially, requiring the exploration of all possible moves and states, which can be computationally expensive for large game trees.

### How can the problem of exponential growth in the minimax algorithm be overcome?

-The problem of exponential growth in the minimax algorithm can be overcome by using alpha-beta pruning, which is discussed in the next video.

### What is the purpose of constructing game trees in the minimax algorithm?

-The purpose of constructing game trees in the minimax algorithm is to visualize and evaluate the optimal moves for each player by exploring all possible game outcomes.

### Outlines

### 🎮 Introduction to Game Playing in Artificial Intelligence

This paragraph introduces the topic of game playing in artificial intelligence (AI), emphasizing its importance as an application of AI. It mentions the complexity of online games and clarifies that the discussion will focus on symbolic game strategies rather than complex games. The paragraph defines a game as consisting of players, rules, moves, and payoffs, which are outcomes for each combination of strategies. It also introduces the concept of utility, which is the payoff awarded to players for winning the game. The speaker then transitions into discussing searching techniques in AI, particularly depth-first search, and contrasts it with breadth-first search. The paragraph concludes by introducing two key searching techniques used in game playing: the minimax algorithm and alpha-beta pruning.

### 🌳 Deep Dive into the Minimax Algorithm

The second paragraph delves into the specifics of the minimax algorithm used in game playing AI. It describes the algorithm as a recursive or backtracking method for decision-making and game theory. The paragraph explains the game tree concept, which is central to the minimax algorithm, and notes that it is applicable to small games due to the manageable search space. The minimax algorithm involves two players, 'max' and 'min', where 'max' aims to maximize the score and 'min' tries to minimize it. The paragraph illustrates how the algorithm works through a game tree example, showing how values are assigned at each level based on the players' turns. It highlights that the algorithm uses depth-first search (DFS) to explore all possible moves and states, leading to exponential growth in complexity. The paragraph concludes by pointing out the inefficiency of the minimax algorithm in large game trees and hints at the solution provided by alpha-beta pruning, which will be discussed in the next video.

### Mindmap

### Keywords

### 💡Game playing

### 💡Artificial Intelligence

### 💡Minimax Algorithm

### 💡Alpha-Beta Pruning

### 💡Game Trees

### 💡Payoff

### 💡Depth First Search

### 💡Backtracking

### 💡Max and Min Players

### 💡Terminal Nodes

### Highlights

Introduction to game playing in artificial intelligence, focusing on strategic aspects of simple, symbolic games rather than complex online games.

A game in AI consists of players, rules, moves, and payoffs, which are the outcomes for each combination of strategies.

Payoff is the utility or outcome awarded to players, such as points for winning.

Depth-first search is used in game playing due to its efficiency over breadth-first search in high branching factor scenarios.

Minimax algorithm and alpha-beta pruning are the two key searching techniques used in game playing AI.

The minimax algorithm is a recursive or backtracking algorithm used for decision-making in game theory.

The algorithm involves two players, Max and Min, where Max aims to maximize the score and Min aims to minimize it.

Game trees are constructed for small games to apply the minimax algorithm, as searching in complex game trees is not feasible.

The minimax algorithm uses depth-first strategy to evaluate the optimal move for each player.

Terminal nodes in the game tree have pre-computed values that determine the payoffs.

The algorithm proceeds level by level, alternating between Max and Min players' turns.

Max selects the maximum value at each level, while Min selects the minimum value to counteract Max.

The minimax algorithm can be visualized through a game tree with nodes representing game states and values representing scores.

The algorithm's challenge is its exponential growth in complexity, requiring evaluation of all possible game states.

Alpha-beta pruning is introduced as a method to overcome the exponential growth problem of the minimax algorithm by eliminating unnecessary branches.

The next video will cover alpha-beta pruning in detail, which is crucial for improving the efficiency of game playing AI.