From 1d527a89cdfac393c38b44a6f388dcea7928d83f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Max=20K=C3=A4nner?= <max.kaenner@gmail.com>
Date: Mon, 21 Apr 2025 21:48:11 +0200
Subject: [PATCH] make simulation faster

---
 battlesnake/src/types/simulation.rs | 84 ++++++++++++++++-------------
 1 file changed, 47 insertions(+), 37 deletions(-)

diff --git a/battlesnake/src/types/simulation.rs b/battlesnake/src/types/simulation.rs
index 2aa9d50..63dd247 100644
--- a/battlesnake/src/types/simulation.rs
+++ b/battlesnake/src/types/simulation.rs
@@ -224,7 +224,7 @@ impl Board {
 
     #[must_use]
     pub fn is_free(&self, tile: Coord) -> bool {
-        if !(tile.x < self.width && tile.y < self.height) {
+        if !self.is_in_bounds(tile) {
             return false;
         }
         let index = self.coord_to_linear(tile);
@@ -286,10 +286,7 @@ impl Board {
     fn valid_actions_index(&self, index: usize) -> impl Iterator<Item = Direction> + use<'_> {
         let head = self.snakes[index].head();
         enum_iterator::all::<Direction>()
-            .map(move |direction| (direction, head.wrapping_apply(direction)))
-            .filter(|(_, tile)| self.is_in_bounds(*tile))
-            .filter(|(_, tile)| self.is_free(*tile))
-            .map(|(direction, _)| direction)
+            .filter(move |direction| self.is_free(head.wrapping_apply(*direction)))
     }
 
     fn move_standard(&mut self, actions: &[(u8, Direction)]) {
@@ -432,44 +429,57 @@ impl Board {
     }
 
     fn spawn_food(&mut self) {
-        let num_food = self.food.count_ones();
-        let needed_food = if num_food < usize::from(self.min_food) {
-            usize::from(self.min_food) - num_food
-        } else {
-            usize::from(
-                self.food_spawn_chance > 0 && rng().random_range(0..100) < self.food_spawn_chance,
-            )
-        };
+        let food_needed = self.check_food_needing_placement();
 
-        if needed_food == 0 {
-            return;
+        if food_needed > 0 {
+            self.place_food_randomly(food_needed);
+        }
+    }
+
+    fn check_food_needing_placement(&self) -> u16 {
+        let min_food = self.min_food;
+        let food_spawn_chance = self.food_spawn_chance;
+        let num_current_food = u16::try_from(self.food.count_ones()).unwrap_or(u16::MAX);
+
+        if num_current_food < min_food {
+            return min_food - num_current_food;
+        }
+        if food_spawn_chance > 0 && (100 - rng().random_range(0..100)) < food_spawn_chance {
+            return 1;
         }
 
-        let food_spots = self
+        0
+    }
+
+    fn place_food_randomly(&mut self, amount: u16) {
+        let tails: Vec<_> = self
+            .snakes
+            .iter()
+            .map(|snake| self.coord_to_linear(snake.tail()))
+            .collect();
+        let possible_moves: Vec<_> = self
+            .snakes
+            .iter()
+            .flat_map(|snake| {
+                let head = snake.head();
+                enum_iterator::all::<Direction>()
+                    .map(move |direction| head.wrapping_apply(direction))
+                    .filter(|tile| self.is_in_bounds(*tile))
+                    .map(|tile| self.coord_to_linear(tile))
+            })
+            .collect();
+        let unoccupied_points = self
             .free
             .iter()
+            .by_vals()
             .enumerate()
-            .filter_map(|(i, free)| free.then_some(i))
-            .filter(|i| {
-                self.snakes
-                    .iter()
-                    .all(|snake| self.coord_to_linear(snake.tail()) != *i)
-            })
-            .filter(|i| {
-                self.snakes
-                    .iter()
-                    .flat_map(|snake| {
-                        let head = snake.head();
-                        enum_iterator::all::<Direction>()
-                            .map(move |direction| head.wrapping_apply(direction))
-                            .filter(|tile| self.is_in_bounds(*tile))
-                    })
-                    .all(|action| *i != self.coord_to_linear(action))
-            })
-            .filter(|i| !self.food[*i])
-            .choose_multiple(&mut rng(), needed_food);
-        for index in food_spots {
-            self.food.set(index, true);
+            .zip(self.hazard.iter().by_vals())
+            .filter_map(|((i, free), hazard)| (!hazard && free).then_some(i))
+            .filter(|i| !tails.contains(i))
+            .filter(|i| !possible_moves.contains(i));
+
+        for food_spot in unoccupied_points.choose_multiple(&mut rng(), usize::from(amount)) {
+            self.food.set(food_spot, true);
         }
     }