reuse old simulation states

battlesnake/src/logic.rs

@@ -48,6 +48,7 @@ struct GameInfo {
     calculation_time: Arc<Mutex<Duration>>,
     token_mapping: Arc<BTreeMap<String, SnakeToken>>,
     my_token: SnakeToken,
+    tree: Arc<Mutex<Option<Node>>>,
 }
 
 static GAME_INFOS: LazyLock<Mutex<HashMap<(String, String), GameInfo>>> =
@@ -70,6 +71,7 @@ pub fn start(game: &Game, _turn: i32, board: &Board, you: &Battlesnake) {
             ))),
             token_mapping,
             my_token,
+            tree: Arc::new(Mutex::new(None)),
         },
     );
 }
@@ -114,6 +116,7 @@ pub fn get_move(
                 ))),
                 token_mapping,
                 my_token,
+                tree: Arc::new(Mutex::new(None)),
             }
         });
 
@@ -126,12 +129,9 @@ pub fn get_move(
         game.ruleset.name == "constrictor",
     );
     let possible_actions = board.possible_actions().get(&game_info.my_token).cloned()?;
-    if possible_actions.len() <= 1 {
-        info!("Only one movement option exists in turn {turn}. Skipping Tree evaluation");
-        return possible_actions.first().map(|direction| Action {
-            r#move: *direction,
-            shout: None,
-        });
+    if possible_actions.is_empty() {
+        info!("No movement options in turn {turn}");
+        return None;
     }
 
     // do some latency compensation
@@ -153,7 +153,45 @@ pub fn get_move(
             },
         );
 
-    let mut tree = Node::default();
+    let mut tree_guard = game_info.tree.lock();
+    let tree = match tree_guard {
+        Err(ref e) => {
+            error!("unable to lock tree: {e}");
+            None
+        }
+        Ok(ref mut guard) => guard.as_mut(),
+    };
+    let mut tree = tree
+        .and_then(|node| {
+            let snake_length_direction: BTreeMap<_, _> = board
+                .snakes()
+                .map(|snake| {
+                    let length = board.snake_length(snake).unwrap_or_default();
+                    let action = board.last_action(snake).unwrap_or(Direction::Up);
+                    (snake, (action, length))
+                })
+                .collect();
+            let node_key = node
+                .childs
+                .keys()
+                .find(|child| {
+                    child.iter().all(|(snake, (direction, length))| {
+                        snake_length_direction
+                            .get(snake)
+                            .copied()
+                            .unwrap_or((*direction, 0))
+                            == (*direction, *length)
+                    })
+                })?
+                .clone();
+            let node = node.childs.remove(&node_key)?;
+            info!(
+                "using previous node with {} simulations",
+                node.statistic.played
+            );
+            Some(node)
+        })
+        .unwrap_or_default();
 
     while Instant::now() < deadline {
         let mut board = board.clone();
@@ -175,6 +213,11 @@ pub fn get_move(
         .map(|(direction, _)| *direction)
         .or_else(|| possible_actions.iter().choose(&mut thread_rng()).copied())?;
 
+    if let Ok(ref mut guard) = tree_guard {
+        **guard = Some(tree);
+    }
+    std::mem::drop(tree_guard);
+
     info!(
         "DIRECTION {turn}: {chosen:?} after {}ms ({})",
         start.elapsed().as_millis(),

battlesnake/src/simulation.rs

@@ -118,6 +118,14 @@ impl Board {
         self.snakes.get(&token).map(|snake| snake.body.len())
     }
 
+    #[must_use]
+    pub fn last_action(&self, token: SnakeToken) -> Option<Direction> {
+        self.snakes.get(&token).and_then(|snake| {
+            enum_iterator::all::<Direction>()
+                .find(|direction| snake.body[1].move_to(*direction) == *snake.head())
+        })
+    }
+
     pub fn simulate_actions(
         &mut self,
         actions: &BTreeMap<SnakeToken, Direction>,
@@ -313,7 +321,6 @@ impl Battlesnake {
 
     #[must_use]
     pub fn head(&self) -> &Coord {
-        debug_assert!(!self.body.is_empty());
-        self.body.front().unwrap_or_else(|| unreachable!())
+        &self.body[0]
     }
 }