correct food spawning algorithm

battlesnake/src/types/simulation.rs

@@ -459,6 +459,17 @@ impl Board {
                     .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 thread_rng(), needed_food);
         for index in food_spots {