optimize compute_values a TON (reduce depth_of calls)... and other stuff

src/complexagent.rs

@@ -1,3 +1,5 @@
+use either::Either;
+
 use crate::{agent::Agent, board::Board, piece::Piece};
 
 #[derive(Clone)]
@@ -137,8 +139,20 @@ impl FutureMoves {
     }
 
     fn compute_values(&mut self) {
+        // PERF! doing this filtering here previously visited moves reduces time
+        // spent in `depth_of` from 27.79% -> 2.9%
+        let mut visited = vec![false; self.arena.len()];
+
         for depth in (0..=self.current_depth).rev() {
             let nodes_at_depth: Vec<usize> = (0..self.arena.len())
+                .filter(|&idx| {
+                    if visited[idx] {
+                        false
+                    } else {
+                        visited[idx] = true;
+                        true
+                    }
+                })
                 .filter(|&idx| self.depth_of(idx) == depth)
                 .collect();
 
@@ -171,18 +185,15 @@ impl FutureMoves {
     }
 
     pub fn best_move(&self) -> Option<(usize, usize)> {
-        let root_nodes = match self.current_root {
-            Some(root) => vec![root],
-            None => self
-                .arena
+        (match self.current_root {
+            Some(root) => Either::Left(vec![root].into_iter()),
+            None => Either::Right(
+                self.arena
                     .iter()
                     .enumerate()
-                .filter_map(|(idx, node)| node.parent.is_none().then_some(idx))
-                .collect(),
-        };
-
-        root_nodes
-            .into_iter()
+                    .filter_map(|(idx, node)| node.parent.is_none().then_some(idx)),
+            ),
+        })
         .map(|idx| &self.arena[idx])
         .max_by_key(|x| x.value)
         .map(|x| (x.i, x.j))
@@ -209,7 +220,12 @@ impl FutureMoves {
         };
 
         let mut retain = vec![false; self.arena.len()];
-        let mut stack = vec![root];
+
+        // stack is going to be AT MAXIMUM, the size of the array,
+        // so lets just pre-allocate it
+        let mut stack = Vec::with_capacity(self.arena.len());
+        stack.push(root);
+
         // traverse children of the current root
         while let Some(idx) = stack.pop() {
             retain[idx] = true;