why clion

src/lib.rs

@@ -4,6 +4,7 @@
 
 use bumpalo::collections::Vec;
 use bumpalo::Bump;
+use std::cell::RefCell;
 
 use rand::Rng;
 
@@ -19,14 +20,14 @@ pub trait GameState {
     fn is_finished(&self) -> bool;
 }
 
-type Tree<'tree, S> = Node<'tree, S>;
+type Tree<'tree, S> = RefCell<Node<'tree, S>>;
 
 struct Node<'tree, S> {
     state: S,
     visited: u64,
-    won: u64,
+    score: u64,
-    parent: Option<&'tree Node<'tree, S>>,
+    parent: Option<&'tree RefCell<Node<'tree, S>>>,
-    children: Vec<'tree, Node<'tree, S>>,
+    children: Vec<'tree, RefCell<Node<'tree, S>>>,
 }
 
 impl<'tree, S: GameState> Node<'tree, S> {
@@ -34,56 +35,70 @@ impl<'tree, S: GameState> Node<'tree, S> {
         Node {
             state,
             visited: 0,
-            won: 0,
+            score: 0,
             parent: None,
             children: Vec::new_in(alloc),
         }
     }
 
-    fn random_child(&self) -> &Self {
+    fn random_child(&self) -> &RefCell<Self> {
         &self.children[rand::thread_rng().gen_range(0..self.children.len())]
     }
 
-    fn into_child_with_max_score(self) -> Self {
+    fn into_child_with_max_score(self) -> Option<RefCell<Self>> {
-        todo!()
+        self.children
+            .into_iter()
+            .max_by_key(|node| node.borrow().score)
     }
 }
 
 mod mcts {
     use crate::{GameState, Node};
     use bumpalo::Bump;
+    use std::cell::RefCell;
 
     const MAX_TRIES: u64 = 10000;
 
     pub fn find_next_move<S: GameState>(current_state: S) -> S {
         let alloc = Bump::new();
 
-        let root_node = Node::new(current_state, &alloc);
+        let root_node = RefCell::new(Node::new(current_state, &alloc));
 
         for _ in 0..MAX_TRIES {
-            let promising_node = select_promising_node(&root_node);
+            let promising_node_cell = select_promising_node(&root_node);
+            let promising_node = promising_node_cell.borrow();
 
             if !promising_node.state.is_finished() {
-                expand_node(promising_node);
+                expand_node(&promising_node);
             }
 
-            let node_to_explore = if !node_to_explore.children.is_empty() {
+            let node_to_explore = if !promising_node.children.is_empty() {
                 promising_node.random_child()
             } else {
-                promising_node
+                promising_node_cell
             };
 
-            let playout_result = simulate_random_playout(node_to_explore);
+            let playout_result = simulate_random_playout(&node_to_explore.borrow());
-            back_propagation(node_to_explore, playout_result);
+            back_propagation(&node_to_explore.borrow(), playout_result);
         }
 
-        let winner_node = root_node.into_child_with_max_score();
+        let winner_node = root_node.into_inner().into_child_with_max_score();
 
-        winner_node.state
+        let state = winner_node.unwrap().into_inner().state;
+        state
     }
 
-    fn select_promising_node<'tree, S>(node: &'tree Node<'_, S>) -> &'tree Node<'tree, S> {
+    fn select_promising_node<'tree, S>(
-        todo!()
+        root_node: &'tree RefCell<Node<'tree, S>>,
+    ) -> &'tree RefCell<Node<'tree, S>> {
+        let mut node = root_node;
+
+        let borrowed_node = node.borrow();
+        while borrowed_node.children.len() != 0 {
+            node = uct::find_best_node_with_uct(&borrowed_node).unwrap()
+        }
+
+        node
     }
 
     fn expand_node<S>(node: &Node<S>) {
@@ -100,6 +115,7 @@ mod mcts {
 
     mod uct {
         use crate::Node;
+        use std::cell::RefCell;
 
         pub fn uct(total_visit: u64, win_score: u64, node_visit: u64) -> u64 {
             if node_visit == 0 {
@@ -113,12 +129,15 @@ mod mcts {
             num as u64
         }
 
-        pub fn find_best_node_with_uct<S>(node: &Node<S>) -> Option<&Node<S>> {
+        pub fn find_best_node_with_uct<'tree, S>(
+            node: &'tree Node<'tree, S>,
+        ) -> Option<&'tree RefCell<Node<'tree, S>>> {
             let parent_visit_count = node.visited;
 
-            node.children
+            node.children.iter().max_by_key(|n| {
-                .iter()
+                let n = n.borrow();
-                .max_by_key(|n| uct(parent_visit_count, n.won, n.visited))
+                uct(parent_visit_count, n.score, n.visited)
+            })
         }
     }
 }