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Lecture 5: Adversarial Search

Game Playing AI: When Your Opponent Fights Back

Master Minimax, Alpha-Beta Pruning, and Game Theory

From Cooperative to Adversarial Search

Traditional search assumes a cooperative environment - only you make moves.

Adversarial search handles competitive games where your opponent actively works against you!

About This Lecture

Adversarial search deals with competitive, multi-agent environments where one agent's success comes at the expense of another. Unlike traditional search where we control all moves, adversarial search must account for an intelligent opponent trying to minimize our success while maximizing their own.

Duration: 2-3 hours
Topics: Game theory & algorithms
Level: Intermediate

Adversarial Search Algorithms

Interactive Exercises & Practice

Advanced Game Playing Techniques

Evaluation Functions

Heuristic functions that estimate position strength when complete search is impossible. Balance material, position, and strategic factors.

Forward Pruning

Aggressive technique that prunes seemingly bad moves without exploring them. Risky but can dramatically speed up search.

Monte Carlo Tree Search

Modern technique using random simulations to evaluate positions. Balances exploration and exploitation dynamically.

Game-Playing Applications

Chess

Classic two-player perfect information game. Deep Blue's victory over Kasparov demonstrated the power of adversarial search with evaluation functions.

Checkers

First game "solved" using adversarial search. Chinook became world champion and proved the game is a draw with perfect play.

Go

Most complex board game tackled by AI. AlphaGo's victory combined Monte Carlo Tree Search with deep neural networks.

Poker

Imperfect information game requiring probabilistic reasoning. Modern AI agents handle uncertainty and bluffing strategies.

Video Games

Real-time strategy games use adversarial search for unit movement, resource allocation, and tactical decision making.

Trading & Auctions

Financial markets and auction systems model competitive environments where agents try to maximize their own utility.

Key Insights: When to Use Adversarial Search

Use Adversarial Search When:
  • Multi-agent environment - opponents actively work against you
  • Zero-sum games - one player's gain is another's loss
  • Turn-based systems with alternating moves
  • Perfect information - all players see the complete state
  • Discrete actions - clear set of possible moves
  • Terminal conditions - games have definite end states
Challenges in Adversarial Search:
  • Exponential growth - game trees grow very quickly
  • Imperfect information - hidden cards, incomplete knowledge
  • Stochastic elements - dice rolls, random events
  • Real-time constraints - limited time to make decisions
  • Complex evaluation - hard to judge position strength
  • Multiple opponents - more than two players