rustic_mcts/examples/auto_tic_tac_toe.rs

use std::collections::HashMap;
use std::fmt;

use rustic_mcts::policy::backprop::BackpropagationPolicy;
use rustic_mcts::policy::decision::DecisionPolicy;
use rustic_mcts::policy::selection::SelectionPolicy;
use rustic_mcts::policy::simulation::SimulationPolicy;
use rustic_mcts::{Action, GameState, MCTSConfig, RewardVal, MCTS};

fn main() {
    println!("MCTS Tic-Tac-Toe Example");
    println!("========================");
    println!();

    // Set up a new game
    let mut game = TicTacToe::new();

    // Create MCTS configuration
    let config = MCTSConfig {
        max_iterations: 10_000,
        max_time: None,
        tree_size_allocation: 10_000,
        selection_policy: SelectionPolicy::UCB1Tuned(1.414),
        simulation_policy: SimulationPolicy::Random,
        backprop_policy: BackpropagationPolicy::Standard,
        decision_policy: DecisionPolicy::MostVisits,
    };

    // Main game loop
    while !game.is_terminal() {
        // Display the board
        println!("{}", game);

        // AI player (O)
        println!("{:?} is thinking...", game.current_player);

        // Create a new MCTS search
        let mut mcts = MCTS::new(game.clone(), &config);

        // Find the best move
        match mcts.search() {
            Ok(action) => {
                println!(
                    "AI chooses: {} (row {}, col {})",
                    action.index,
                    action.index / 3,
                    action.index % 3
                );

                // Apply the AI's move
                game = game.state_after_action(&action);
            }
            Err(e) => {
                println!("Error: {:?}", e);
                break;
            }
        }
    }

    // Display final state
    println!("{}", game);

    // Report the result
    if let Some(winner) = game.get_winner() {
        println!("Player {:?} wins!", winner);
    } else {
        println!("The game is a draw!");
    }
}

/// Players in Tic-Tac-Toe
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
enum Player {
    X,
    O,
}

impl rustic_mcts::Player for Player {}

/// Tic-Tac-Toe move
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
struct Move {
    /// Board position index (0-8)
    index: usize,
}

impl Action for Move {
    fn id(&self) -> usize {
        self.index
    }
}

/// Tic-Tac-Toe game state
#[derive(Clone)]
struct TicTacToe {
    /// Board representation (None = empty, Some(Player) = occupied)
    board: [Option<Player>; 9],

    /// Current player's turn
    current_player: Player,

    /// Number of moves played so far
    moves_played: usize,
}

impl TicTacToe {
    /// Creates a new empty Tic-Tac-Toe board
    fn new() -> Self {
        TicTacToe {
            board: [None; 9],
            current_player: Player::X,
            moves_played: 0,
        }
    }

    /// Returns the winner of the game, if any
    fn get_winner(&self) -> Option<Player> {
        // Check rows
        for row in 0..3 {
            let i = row * 3;
            if self.board[i].is_some()
                && self.board[i] == self.board[i + 1]
                && self.board[i] == self.board[i + 2]
            {
                return self.board[i];
            }
        }

        // Check columns
        for col in 0..3 {
            if self.board[col].is_some()
                && self.board[col] == self.board[col + 3]
                && self.board[col] == self.board[col + 6]
            {
                return self.board[col];
            }
        }

        // Check diagonals
        if self.board[0].is_some()
            && self.board[0] == self.board[4]
            && self.board[0] == self.board[8]
        {
            return self.board[0];
        }
        if self.board[2].is_some()
            && self.board[2] == self.board[4]
            && self.board[2] == self.board[6]
        {
            return self.board[2];
        }

        None
    }
}

impl GameState for TicTacToe {
    type Action = Move;
    type Player = Player;

    fn get_legal_actions(&self) -> Vec<Self::Action> {
        let mut actions = Vec::new();
        for i in 0..9 {
            if self.board[i].is_none() {
                actions.push(Move { index: i });
            }
        }
        actions
    }

    fn state_after_action(&self, action: &Self::Action) -> Self {
        let mut new_state = self.clone();

        // Make the move
        new_state.board[action.index] = Some(self.current_player);
        new_state.moves_played = self.moves_played + 1;

        // Switch player
        new_state.current_player = match self.current_player {
            Player::X => Player::O,
            Player::O => Player::X,
        };

        new_state
    }

    fn is_terminal(&self) -> bool {
        self.get_winner().is_some() || self.moves_played == 9
    }

    fn reward_for_player(&self, player: &Self::Player) -> RewardVal {
        if let Some(winner) = self.get_winner() {
            if winner == *player {
                return 1.0; // Win
            } else {
                return 0.0; // Loss
            }
        }

        // Draw
        0.5
    }

    fn rewards_for_players(&self) -> HashMap<Self::Player, RewardVal> {
        HashMap::from_iter(vec![
            (Player::X, self.reward_for_player(&Player::X)),
            (Player::O, self.reward_for_player(&Player::O)),
        ])
    }

    fn get_current_player(&self) -> &Self::Player {
        &self.current_player
    }
}

impl fmt::Display for TicTacToe {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        writeln!(f, "  0 1 2")?;
        for row in 0..3 {
            write!(f, "{} ", row)?;
            for col in 0..3 {
                let index = row * 3 + col;
                let symbol = match self.board[index] {
                    Some(Player::X) => "X",
                    Some(Player::O) => "O",
                    None => ".",
                };
                write!(f, "{} ", symbol)?;
            }
            writeln!(f)?;
        }

        writeln!(f, "\nPlayer {:?}'s turn", self.current_player)?;
        Ok(())
    }
}

impl fmt::Debug for TicTacToe {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "\n")?;
        for row in 0..3 {
            for col in 0..3 {
                let index = row * 3 + col;
                let symbol = match self.board[index] {
                    Some(Player::X) => "X",
                    Some(Player::O) => "O",
                    None => ".",
                };
                write!(f, "{} ", symbol)?;
            }
            writeln!(f)?;
        }
        Ok(())
    }
}