Updated rust dependencies

GameState::reward_for_player is no longer a trait function
We need GameState::rewards_for_players implemented, the library currently doesn't need to specify for a singular player.
2026-07-07 12:29:54 -07:00 · 2025-06-30 21:41:49 -07:00 · 2025-06-30 21:41:27 -07:00 · 2025-06-30 20:08:18 -07:00 · 2025-06-29 22:51:17 -07:00 · 2025-06-29 22:50:54 -07:00
12 changed files with 517 additions and 168 deletions
@@ -3,27 +3,113 @@
 version = 4

 [[package]]
-name = "cfg-if"
-version = "1.0.1"
+name = "anstyle"
+version = "1.0.14"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9555578bc9e57714c812a1f84e4fc5b4d21fcb063490c624de019f7464c91268"
+checksum = "940b3a0ca603d1eade50a4846a2afffd5ef57a9feac2c0e2ec2e14f9ead76000"
+
+[[package]]
+name = "bitflags"
+version = "2.13.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b4388bee8683e3d04af747c73422af53102d2bd24d9eadb6cbc100baef4b43f8"
+
+[[package]]
+name = "cfg-if"
+version = "1.0.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9330f8b2ff13f34540b44e946ef35111825727b38d33286ef986142615121801"
+
+[[package]]
+name = "clap"
+version = "4.6.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1ddb117e43bbf7dacf0a4190fef4d345b9bad68dfc649cb349e7d17d28428e51"
+dependencies = [
+ "clap_builder",
+]
+
+[[package]]
+name = "clap_builder"
+version = "4.6.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "714a53001bf66416adb0e2ef5ac857140e7dc3a0c48fb28b2f10762fc4b5069f"
+dependencies = [
+ "anstyle",
+ "clap_lex",
+ "terminal_size",
+]
+
+[[package]]
+name = "clap_lex"
+version = "1.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c8d4a3bb8b1e0c1050499d1815f5ab16d04f0959b233085fb31653fbfc9d98f9"
+
+[[package]]
+name = "condtype"
+version = "1.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "baf0a07a401f374238ab8e2f11a104d2851bf9ce711ec69804834de8af45c7af"
+
+[[package]]
+name = "divan"
+version = "0.1.21"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a405457ec78b8fe08b0e32b4a3570ab5dff6dd16eb9e76a5ee0a9d9cbd898933"
+dependencies = [
+ "cfg-if",
+ "clap",
+ "condtype",
+ "divan-macros",
+ "libc",
+ "regex-lite",
+]
+
+[[package]]
+name = "divan-macros"
+version = "0.1.21"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9556bc800956545d6420a640173e5ba7dfa82f38d3ea5a167eb555bc69ac3323"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "errno"
+version = "0.3.14"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "39cab71617ae0d63f51a36d69f866391735b51691dbda63cf6f96d042b63efeb"
+dependencies = [
+ "libc",
+ "windows-sys",
+]

 [[package]]
 name = "getrandom"
-version = "0.2.16"
+version = "0.3.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "335ff9f135e4384c8150d6f27c6daed433577f86b4750418338c01a1a2528592"
+checksum = "899def5c37c4fd7b2664648c28120ecec138e4d395b459e5ca34f9cce2dd77fd"
 dependencies = [
 "cfg-if",
 "libc",
- "wasi",
+ "r-efi",
+ "wasip2",
 ]

 [[package]]
 name = "libc"
-version = "0.2.174"
+version = "0.2.186"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "1171693293099992e19cddea4e8b849964e9846f4acee11b3948bcc337be8776"
+checksum = "68ab91017fe16c622486840e4c83c9a37afeff978bd239b5293d61ece587de66"
+
+[[package]]
+name = "linux-raw-sys"
+version = "0.12.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "32a66949e030da00e8c7d4434b251670a91556f4144941d37452769c25d58a53"

 [[package]]
 name = "ppv-lite86"
@@ -36,38 +122,43 @@ dependencies = [

 [[package]]
 name = "proc-macro2"
-version = "1.0.95"
+version = "1.0.106"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "02b3e5e68a3a1a02aad3ec490a98007cbc13c37cbe84a3cd7b8e406d76e7f778"
+checksum = "8fd00f0bb2e90d81d1044c2b32617f68fcb9fa3bb7640c23e9c748e53fb30934"
 dependencies = [
 "unicode-ident",
 ]

 [[package]]
 name = "quote"
-version = "1.0.40"
+version = "1.0.46"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "1885c039570dc00dcb4ff087a89e185fd56bae234ddc7f056a945bf36467248d"
+checksum = "dfbc457d0c7a0759a614551b11a6409e5951f6c7537be1f1b7682b9ae9230368"
 dependencies = [
 "proc-macro2",
 ]

 [[package]]
-name = "rand"
-version = "0.8.5"
+name = "r-efi"
+version = "5.3.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "34af8d1a0e25924bc5b7c43c079c942339d8f0a8b57c39049bef581b46327404"
+checksum = "69cdb34c158ceb288df11e18b4bd39de994f6657d83847bdffdbd7f346754b0f"
+
+[[package]]
+name = "rand"
+version = "0.9.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "44c5af06bb1b7d3216d91932aed5265164bf384dc89cd6ba05cf59a35f5f76ea"
 dependencies = [
- "libc",
 "rand_chacha",
 "rand_core",
 ]

 [[package]]
 name = "rand_chacha"
-version = "0.3.1"
+version = "0.9.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e6c10a63a0fa32252be49d21e7709d4d4baf8d231c2dbce1eaa8141b9b127d88"
+checksum = "d3022b5f1df60f26e1ffddd6c66e8aa15de382ae63b3a0c1bfc0e4d3e3f325cb"
 dependencies = [
 "ppv-lite86",
 "rand_core",
@@ -75,26 +166,46 @@ dependencies = [

 [[package]]
 name = "rand_core"
-version = "0.6.4"
+version = "0.9.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "ec0be4795e2f6a28069bec0b5ff3e2ac9bafc99e6a9a7dc3547996c5c816922c"
+checksum = "76afc826de14238e6e8c374ddcc1fa19e374fd8dd986b0d2af0d02377261d83c"
 dependencies = [
 "getrandom",
 ]

+[[package]]
+name = "regex-lite"
+version = "0.1.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cab834c73d247e67f4fae452806d17d3c7501756d98c8808d7c9c7aa7d18f973"
+
 [[package]]
 name = "rustic_mcts"
 version = "0.1.0"
 dependencies = [
+ "divan",
 "rand",
 "thiserror",
 ]

 [[package]]
-name = "syn"
-version = "2.0.103"
+name = "rustix"
+version = "1.1.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e4307e30089d6fd6aff212f2da3a1f9e32f3223b1f010fb09b7c95f90f3ca1e8"
+checksum = "b6fe4565b9518b83ef4f91bb47ce29620ca828bd32cb7e408f0062e9930ba190"
+dependencies = [
+ "bitflags",
+ "errno",
+ "libc",
+ "linux-raw-sys",
+ "windows-sys",
+]
+
+[[package]]
+name = "syn"
+version = "2.0.118"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1b9ae57f904213ebb649ce6895b8a66c66f0203b9319718f69a5612a065b1422"
 dependencies = [
 "proc-macro2",
 "quote",
@@ -102,19 +213,29 @@ dependencies = [
 ]

 [[package]]
-name = "thiserror"
-version = "2.0.12"
+name = "terminal_size"
+version = "0.4.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "567b8a2dae586314f7be2a752ec7474332959c6460e02bde30d702a66d488708"
+checksum = "230a1b821ccbd75b185820a1f1ff7b14d21da1e442e22c0863ea5f08771a8874"
+dependencies = [
+ "rustix",
+ "windows-sys",
+]
+
+[[package]]
+name = "thiserror"
+version = "2.0.18"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4288b5bcbc7920c07a1149a35cf9590a2aa808e0bc1eafaade0b80947865fbc4"
 dependencies = [
 "thiserror-impl",
 ]

 [[package]]
 name = "thiserror-impl"
-version = "2.0.12"
+version = "2.0.18"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "7f7cf42b4507d8ea322120659672cf1b9dbb93f8f2d4ecfd6e51350ff5b17a1d"
+checksum = "ebc4ee7f67670e9b64d05fa4253e753e016c6c95ff35b89b7941d6b856dec1d5"
 dependencies = [
 "proc-macro2",
 "quote",
@@ -123,30 +244,54 @@ dependencies = [

 [[package]]
 name = "unicode-ident"
-version = "1.0.18"
+version = "1.0.24"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "5a5f39404a5da50712a4c1eecf25e90dd62b613502b7e925fd4e4d19b5c96512"
+checksum = "e6e4313cd5fcd3dad5cafa179702e2b244f760991f45397d14d4ebf38247da75"

 [[package]]
-name = "wasi"
-version = "0.11.1+wasi-snapshot-preview1"
+name = "wasip2"
+version = "1.0.4+wasi-0.2.12"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "ccf3ec651a847eb01de73ccad15eb7d99f80485de043efb2f370cd654f4ea44b"
+checksum = "b67efb37e106e55ce722a510d6b5f9c17f083e5fc79afc2badeb12cc313d9487"
+dependencies = [
+ "wit-bindgen",
+]
+
+[[package]]
+name = "windows-link"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f0805222e57f7521d6a62e36fa9163bc891acd422f971defe97d64e70d0a4fe5"
+
+[[package]]
+name = "windows-sys"
+version = "0.61.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ae137229bcbd6cdf0f7b80a31df61766145077ddf49416a728b02cb3921ff3fc"
+dependencies = [
+ "windows-link",
+]
+
+[[package]]
+name = "wit-bindgen"
+version = "0.57.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1ebf944e87a7c253233ad6766e082e3cd714b5d03812acc24c318f549614536e"

 [[package]]
 name = "zerocopy"
-version = "0.8.26"
+version = "0.8.53"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "1039dd0d3c310cf05de012d8a39ff557cb0d23087fd44cad61df08fc31907a2f"
+checksum = "75726053136156d419e285b9b7eddaaea9e3fea6ce32eed44a89901f0bd98de1"
 dependencies = [
 "zerocopy-derive",
 ]

 [[package]]
 name = "zerocopy-derive"
-version = "0.8.26"
+version = "0.8.53"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9ecf5b4cc5364572d7f4c329661bcc82724222973f2cab6f050a4e5c22f75181"
+checksum = "4714fd92cf900833d49538023a9b3915155210801d1c1169eba513b2addefd71"
 dependencies = [
 "proc-macro2",
 "quote",
@@ -12,5 +12,12 @@ categories = ["algorithms", "data-structures"]


 [dependencies]
-rand = "~0.8"
+rand = "~0.9"
 thiserror = "~2.0"
+
+[dev-dependencies]
+divan = "~0.1"
+
+[[bench]]
+name = "e2e"
+harness = false
@@ -0,0 +1,187 @@
+use std::collections::HashMap;
+
+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() {
+    // Run registered benchmarks.
+    divan::main();
+}
+
+#[divan::bench]
+fn tic_tac_toe() {
+    // 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() {
+        // Create a new MCTS search
+        let mut mcts = MCTS::new(game.clone(), &config);
+
+        // Find the best move
+        match mcts.search() {
+            Ok(action) => {
+                // Apply the AI's move
+                game = game.state_after_action(&action);
+            }
+            Err(_) => {
+                break;
+            }
+        }
+    }
+}
+
+/// 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 {}
+
+/// Tic-Tac-Toe game state
+#[derive(Debug, 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
+    }
+
+    fn reward_for_player(&self, player: &Player) -> RewardVal {
+        if let Some(winner) = self.get_winner() {
+            if winner == *player {
+                return 1.0; // Win
+            } else {
+                return 0.0; // Loss
+            }
+        }
+
+        // Draw
+        0.5
+    }
+}
+
+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 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
+    }
+}
@@ -84,11 +84,7 @@ struct Move {
    index: usize,
 }

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

 /// Tic-Tac-Toe game state
 #[derive(Clone)]
@@ -152,6 +148,19 @@ impl TicTacToe {

        None
    }
+
+    fn reward_for_player(&self, player: &Player) -> RewardVal {
+        if let Some(winner) = self.get_winner() {
+            if winner == *player {
+                return 1.0; // Win
+            } else {
+                return 0.0; // Loss
+            }
+        }
+
+        // Draw
+        0.5
+    }
 }

 impl GameState for TicTacToe {
@@ -188,19 +197,6 @@ impl GameState for TicTacToe {
        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)),
@@ -119,11 +119,7 @@ struct Move {
    index: usize,
 }

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

 /// Tic-Tac-Toe game state
 #[derive(Clone)]
@@ -195,6 +191,19 @@ impl TicTacToe {

        None
    }
+
+    fn reward_for_player(&self, player: &Player) -> RewardVal {
+        if let Some(winner) = self.get_winner() {
+            if winner == *player {
+                return 1.0; // Win
+            } else {
+                return 0.0; // Loss
+            }
+        }
+
+        // Draw
+        0.5
+    }
 }

 impl GameState for TicTacToe {
@@ -231,19 +240,6 @@ impl GameState for TicTacToe {
        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)),
@@ -6,7 +6,8 @@ use crate::policy::simulation::simulate_reward;
 use crate::state::GameState;
 use crate::tree::arena::Arena;
 use crate::tree::node::{Node, RewardVal};
-use rand::prelude::SliceRandom;
+use crate::tree::print_tree;
+use rand::prelude::IndexedRandom;
 use std::collections::HashMap;
 use std::time::Instant;

@@ -74,8 +75,15 @@ impl<'conf, S: GameState + std::fmt::Debug> MCTS<'conf, S> {
        if !selected_node.state.is_terminal() {
            self.expand(selected_id);
            let children: &Vec<usize> = &self.arena.get_node(selected_id).children;
-            let random_child: usize = *children.choose(&mut rand::thread_rng()).unwrap();
-            selected_id = random_child;
+            match children.choose(&mut rand::rng()) {
+                Some(&random_child) => {
+                    selected_id = random_child;
+                }
+                None => {
+                    // We ran out of nodes
+                    return Err(MCTSError::NonTerminalGame);
+                }
+            }
        }
        let rewards = self.simulate(selected_id);
        self.backprop(selected_id, &rewards);
@@ -130,6 +138,10 @@ impl<'conf, S: GameState + std::fmt::Debug> MCTS<'conf, S> {
            None => Err(MCTSError::NoBestAction),
        }
    }
+
+    pub fn print_tree(&self) {
+        print_tree(self.root_id, &self.arena)
+    }
 }

 /// Errors returned by the MCTS algorithm
@@ -69,18 +69,14 @@ fn standard_backprop<S: GameState>(
    let mut current_id: usize = node_id;
    loop {
        let node = arena.get_node_mut(current_id);
-        let player = node.state.get_current_player().clone();
-        match rewards.get(&player) {
-            Some(reward) => {
-                node.increment_visits();
-                node.record_player_reward(player, *reward);
-                if let Some(parent_id) = node.parent {
-                    current_id = parent_id;
-                } else {
-                    break;
-                }
-            }
-            None => (),
+        node.increment_visits();
+        for (player, reward) in rewards.iter() {
+            node.record_player_reward(player.clone(), *reward);
+        }
+        if let Some(parent_id) = node.parent {
+            current_id = parent_id;
+        } else {
+            break;
        }
    }
 }
@@ -94,19 +90,14 @@ fn weighted_backprop<S: GameState>(
    let mut current_id: usize = node_id;
    loop {
        let node = arena.get_node_mut(current_id);
-        let player = node.state.get_current_player().clone();
        let weight = weight_for_depth(depth_factor, node.depth);
-        match rewards.get(&player) {
-            Some(reward) => {
-                node.increment_visits();
-                node.record_player_reward(player, (*reward) * weight);
-                if let Some(parent_id) = node.parent {
-                    current_id = parent_id;
-                } else {
-                    break;
-                }
-            }
-            None => (),
+        for (player, reward) in rewards.iter() {
+            node.record_player_reward(player.clone(), (*reward) * weight);
+        }
+        if let Some(parent_id) = node.parent {
+            current_id = parent_id;
+        } else {
+            break;
        }
    }
 }
@@ -36,15 +36,15 @@ pub fn select_best_child<S: GameState>(
                exploration_constant,
                parent_visits,
                node_a.visits,
-                node_a.rewards(player),
                node_a.reward_average(player),
+                node_a.reward_variance(player),
            );
            let ucb_b = ucb1_tuned_value(
                exploration_constant,
                parent_visits,
                node_b.visits,
-                node_b.rewards(player),
                node_b.reward_average(player),
+                node_b.reward_variance(player),
            );
            ucb_a.partial_cmp(&ucb_b).unwrap()
        })
@@ -57,41 +57,31 @@ pub fn ucb1_tuned_value(
    exploration_constant: f64,
    parent_visits: u64,
    child_visits: u64,
-    child_rewards: Option<&Vec<RewardVal>>,
    reward_avg: RewardVal,
+    reward_variance: f64,
 ) -> RewardVal {
-    match child_rewards {
-        None => {
-            RewardVal::INFINITY // Always explore nodes that have never been visited
-        }
-        Some(child_rewards) => {
-            if child_visits == 0 {
-                RewardVal::INFINITY // Always explore nodes that have never been visited
-            } else {
-                let parent_visits: RewardVal = parent_visits as RewardVal;
-                let child_visits: RewardVal = child_visits as RewardVal;
+    if child_visits == 0 {
+        RewardVal::INFINITY // Always explore nodes that have never been visited
+    } else {
+        let parent_visits: RewardVal = parent_visits as RewardVal;
+        let child_visits: RewardVal = child_visits as RewardVal;

-                // N: number of visits to the parent node
-                // n: number of visits to the child node
-                // x_i: reward of the ith visit to the child node
-                // X: average reward of the child
-                // C: exploration constant
-                //
-                // UCB1-Tuned = X + C * sqrt(Ln(parent_visits) / child_visits * min(1/4, V_n)
-                //   V(n) = sum(x_i^2)/n - X^2 + sqrt(2*ln(N)/n)
-                let exploitation = reward_avg;
-                let mut variance = (child_rewards.iter().map(|&x| x * x).sum::<RewardVal>()
-                    / child_visits)
-                    - (reward_avg * reward_avg)
-                    + (2.0 * parent_visits.ln() / child_visits).sqrt();
-                if variance > 0.25 {
-                    variance = 0.25;
-                }
-                let exploration =
-                    exploration_constant * (parent_visits.ln() / child_visits * variance).sqrt();
-
-                exploitation + exploration
-            }
+        // N: number of visits to the parent node
+        // n: number of visits to the child node
+        // x_i: reward of the ith visit to the child node
+        // X: average reward of the child
+        // C: exploration constant
+        //
+        // UCB1-Tuned = X + C * sqrt(Ln(parent_visits) / child_visits * min(1/4, V_n)
+        //   V(n) = sum(x_i^2)/n - X^2 + sqrt(2*ln(N)/n)
+        let exploitation = reward_avg;
+        let mut variance = reward_variance + (2.0 * parent_visits.ln() / child_visits).sqrt();
+        if variance > 0.25 {
+            variance = 0.25;
        }
+        let exploration =
+            exploration_constant * (parent_visits.ln() / child_visits * variance).sqrt();
+
+        exploitation + exploration
    }
 }
@@ -4,14 +4,14 @@

 use crate::state::GameState;
 use crate::tree::node::{Node, RewardVal};
-use rand::prelude::SliceRandom;
+use rand::prelude::IndexedRandom;
 use std::collections::HashMap;

 pub fn simulate<S: GameState>(node: &Node<S>) -> HashMap<S::Player, RewardVal> {
    let mut state: S = node.state.clone();
    while !state.is_terminal() {
        let legal_actions = state.get_legal_actions();
-        let action = legal_actions.choose(&mut rand::thread_rng()).unwrap();
+        let action = legal_actions.choose(&mut rand::rng()).unwrap();
        state = state.state_after_action(&action);
    }
    state.rewards_for_players()
@@ -7,7 +7,7 @@ use std::hash::Hash;
 ///
 /// When leveraging MCTS for your game, you must implement this trait to provide
 /// the specifics for your game.
-pub trait GameState: Clone {
+pub trait GameState: Clone + Debug {
    /// The type of actions that can be taken in the game
    type Action: Action;

@@ -40,11 +40,11 @@ pub trait GameState: Clone {
    /// instead should modify a copy of the state and return that.
    fn state_after_action(&self, action: &Self::Action) -> Self;

-    /// Returns the reward from the perspective of the given player for the game state
+    /// Returns the rewards for all players from their perspective for the game state
    ///
-    /// This evaluates the current state from the perspective of the given player, and
-    /// returns the reward indicating how good of a result the given state is for the
-    /// player.
+    /// This evaluates the current state from the perspective of each player, and
+    /// returns a HashMap mapping each player to the result of this evaluation, which
+    /// we call the reward.
    ///
    /// This is used in the MCTS backpropagation and simulation phases to evaluate
    /// the value of a given node in the search tree.
@@ -55,9 +55,6 @@ pub trait GameState: Clone {
    /// - 0.0 => a loss for the player
    ///
    /// Other values can be used for relative wins or losses
-    fn reward_for_player(&self, player: &Self::Player) -> RewardVal;
-
-    /// Returns the rewards for all players at the current state
    fn rewards_for_players(&self) -> HashMap<Self::Player, RewardVal>;

    /// Returns the player whose turn it is for the game state
@@ -72,10 +69,7 @@ pub trait GameState: Clone {
 ///
 /// An action is dependent upon the specific game being defined, and includes
 /// things like moves, attacks, and other decisions.
-pub trait Action: Clone + Debug {
-    /// Returns a uniqie identifier for this action
-    fn id(&self) -> usize;
-}
+pub trait Action: Clone + Debug {}

 /// Trait used for players participating in a game
 pub trait Player: Clone + Debug + PartialEq + Eq + Hash {}
@@ -1,2 +1,27 @@
 pub mod arena;
 pub mod node;
+
+use crate::state::GameState;
+use crate::tree::arena::Arena;
+use crate::tree::node::Node;
+
+pub fn print_tree<S: GameState>(node_id: usize, arena: &Arena<S>) {
+    let mut to_print: Vec<usize> = Vec::new();
+    to_print.push(node_id);
+    while let Some(node_id) = to_print.pop() {
+        let node: &Node<S> = arena.get_node(node_id);
+        if node.depth > 0 {
+            for _ in 0..node.depth - 1 {
+                print!("|  ")
+            }
+            print!("|- ");
+        }
+        println!(
+            "{:?} a:{:?} v:{}  {:?}",
+            node_id, node.action, node.visits, node.player_view
+        );
+        for child_id in node.children.iter().rev() {
+            to_print.push(*child_id);
+        }
+    }
+}
@@ -1,5 +1,4 @@
 use std::collections::HashMap;
-use std::fmt::Debug;

 use crate::state::GameState;

@@ -15,7 +14,7 @@ pub type RewardVal = f64;
 ///
 /// This class is not thread safe, as the library does not provide for parallel
 /// search.
-#[derive(Debug)]
+#[derive(std::fmt::Debug)]
 pub struct Node<S: GameState> {
    /// The game state at the given node, after `action`
    pub state: S,
@@ -30,7 +29,7 @@ pub struct Node<S: GameState> {
    pub visits: u64,

    /// The player's evaluation of the node
-    pub player_view: HashMap<S::Player, PlayerNodeView>,
+    pub player_view: HashMap<S::Player, PlayerRewardView>,

    /// The depth of the node in the tree, this is 0 for the root node
    pub depth: usize,
@@ -70,10 +69,10 @@ impl<S: GameState> Node<S> {
        }
    }

-    pub fn rewards(&self, player: &S::Player) -> Option<&Vec<RewardVal>> {
+    pub fn reward_variance(&self, player: &S::Player) -> f64 {
        match self.player_view.get(player) {
-            Some(pv) => Some(&pv.rewards),
-            None => None,
+            Some(pv) => pv.weighted_variance / self.visits as f64,
+            None => 0.0,
        }
    }

@@ -82,37 +81,44 @@ impl<S: GameState> Node<S> {
    }

    pub fn record_player_reward(&mut self, player: S::Player, reward: RewardVal) {
-        let pv = self
-            .player_view
-            .entry(player)
-            .or_insert(PlayerNodeView::default());
-        pv.rewards.push(reward);
+        let pv = self.player_view.entry(player).or_default();
+        let prev_reward_average = pv.reward_average;
        pv.reward_sum += reward;
-        pv.reward_average = pv.reward_sum / pv.rewards.len() as f64;
+        pv.reward_average = pv.reward_sum / self.visits as f64;
+        pv.weighted_variance += (reward - prev_reward_average) * (reward - pv.reward_average);
    }
 }

 /// A player's specific perspective of a node's value
 ///
 /// Each player has their own idea of the value of a node.
-#[derive(Debug)]
-pub struct PlayerNodeView {
+pub struct PlayerRewardView {
    /// The total reward from simulations through this node
    pub reward_sum: RewardVal,

    /// The average reward from simulations through this node, often called the node value
    pub reward_average: RewardVal,

-    /// The rewards we have gotten so far for simulations through this node
-    pub rewards: Vec<RewardVal>,
+    /// The weighted variance from simulations through this node
+    ///
+    /// This is used to calculate online sample variance.
+    /// See Donald E. Knuth. Seminumerical Algorithms, volume 2 of The Art of Computer Programming, chapter 4.2.2, page 232
+    pub weighted_variance: f64,
 }

-impl Default for PlayerNodeView {
+impl Default for PlayerRewardView {
    fn default() -> Self {
-        PlayerNodeView {
+        PlayerRewardView {
            reward_sum: 0.0,
            reward_average: 0.0,
-            rewards: Vec::new(),
+            weighted_variance: 0.0,
        }
    }
 }
+
+impl std::fmt::Debug for PlayerRewardView {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{{sum={} avg={}}}", self.reward_sum, self.reward_average)?;
+        Ok(())
+    }
+}
Author	SHA1	Message	Date
krugd	3676838082	Updated rust dependencies	2026-07-07 12:29:54 -07:00
krugd	6aa9002e92	GameState::reward_for_player is no longer a trait function We need GameState::rewards_for_players implemented, the library currently doesn't need to specify for a singular player.	2025-06-30 21:41:49 -07:00
krugd	76051cd76b	Removing the id field from the Action trait This would in theory be useful for a transposition table, but we do not currently support that. As such I don't want to burden the implementation with that field until it is deemed necessary.	2025-06-30 21:41:27 -07:00
krugd	a7102a0e44	Fixed missing non terminal error	2025-06-30 20:08:18 -07:00
krugd	a2711f341f	Cleanup debug print	2025-06-29 22:51:17 -07:00
krugd	48c93fa197	Renamed the benchmark file	2025-06-29 22:50:54 -07:00
krugd	854772a63d	Improve UCB1-Tuned performance We calculate the sample variance of the rewards online storing the value in the node. This greatly reduces the amount of summations that need to be done to calculate the variance during the selection phase. While this burdens other selection algorithms, the cost is not substantial.	2025-06-29 18:43:52 -07:00
krugd	44ef9ebdd8	Adding really stupid benchmark	2025-06-27 22:25:56 -07:00
krugd	6a33818238	We propagate the reward for both sides The AI now properly choses the optimal path for the active player	2025-06-27 16:12:40 -07:00
krugd	0f9d4f0c4e	Use Entry::or_default	2025-06-27 15:40:58 -07:00
krugd	9f893b0005	Upgrade rand to ~0.9	2025-06-27 15:17:45 -07:00
krugd	b80f039b93	Adding a basic print_tree function to visualize the MCTS search tree This probably is not a good thing to run on a very large tree.	2025-06-27 15:00:43 -07:00