Optimize combines by storing the closest house in a direction.

This is a huge speedup. It's equivalent to using prefix sums. Needs a lot of memory.

src/city.rs

@@ -38,29 +38,37 @@ impl City {
         City { prices, buyable_house_count, width, height }
     }
 
+    #[inline]
     pub fn get_price(&self, house: House) -> u16 {
         self.prices[house.y * self.width + house.x]
     }
 
+    #[inline]
     pub fn get_price_xy(&self, x: usize, y: usize) -> u16 {
         self.prices[y * self.width + x]
     }
 
+    #[inline]
     pub fn is_house(&self, house: House) -> bool {
         self.get_price(house) > 0
     }
 
+    #[inline]
     pub fn is_house_xy(&self, x: usize, y: usize) -> bool {
         self.get_price_xy(x, y) > 0
     }
 
+    #[inline]
     pub fn get_house_count(&self) -> usize {
         self.buyable_house_count
     }
 
+    #[inline]
     pub fn width(&self) -> usize {
         self.width
     }
+
+    #[inline]
     pub fn height(&self) -> usize {
         self.height
     }
@@ -188,6 +196,10 @@ impl<'a> HouseLayout<'a> {
     pub fn houses(&self) -> &Vec<House> {
         &self.houses
     }
+
+    pub fn covered_houses(&self) -> usize {
+        self.reachable_houses
+    }
 }
 
 pub fn get_price(city: &City, houses: &Vec<House>) -> u32 {
@@ -226,6 +238,45 @@ pub fn is_valid(city: &City, houses: &Vec<House>) -> Option<u32> {
     Some(price)
 }
 
+pub struct HouseDistances {
+    width: usize,
+    height: usize,
+    closest_house: Vec<Option<House>>,
+}
+
+impl HouseDistances {
+    pub fn get_closest_house(&self, house: House) -> Option<House> {
+        self.closest_house[house.y * self.width + house.x]
+    }
+
+    pub fn get_closest_house_xy(&self, x: usize, y: usize) -> Option<House> {
+        self.closest_house[y * self.width + x]
+    }
+}
+
+pub fn build_distances_right(city: &City) -> HouseDistances {
+    let mut closest = vec![None; city.width() * city.height()];
+
+    for y in 0..city.height() {
+        let mut last_house_x = None;
+        for x in (0..city.width()).rev() {
+            closest[y * city.width() + x] = match last_house_x {
+                None => None,
+                Some(last_x) => Some(House::new(last_x, y))
+            };
+            if city.is_house_xy(x, y) {
+                last_house_x = Some(x)
+            }
+        }
+    }
+
+    HouseDistances {
+        width: city.width,
+        height: city.height,
+        closest_house: closest
+    }
+}
+
 #[cfg(test)]
 mod tests {
     //use super::*;

src/combine.rs

@@ -1,6 +1,6 @@
 use crate::city;
 use crate::db::{SqliteLayoutDB, SavedLayout, MergeLowerBound, LayoutDB};
-use crate::city::{City, House};
+use crate::city::{City, House, HouseDistances};
 use itertools::Itertools;
 use itertools::iproduct;
 use std::collections::{VecDeque, HashMap};
@@ -60,13 +60,19 @@ pub fn iterate_combines<TDB: LayoutDB>(mut db: &mut TDB, top_layout_count: usize
     let transposed_city = transpose_city(&city);
     if print_progress { eprintln!("Finished building a transposed city"); }
 
+    if print_progress { eprintln!("Building right distances..."); }
+    let right_distances = city::build_distances_right(&city);
+    if print_progress { eprintln!("Building right distances (transposed)..."); }
+    let right_distances_transposed = city::build_distances_right(&city);
+    if print_progress { eprintln!("Finished building right distances"); }
+
     let mut last_improve_step = LastStep::None;
     loop {
         if last_improve_step == LastStep::Vertical { break; }
         if print_progress { eprintln!("Starting to combine {} top houses DB; vertical cuts", top_layout_count); }
 
         let chosen_layouts = choose_layouts(db, &city, top_layout_count);
-        if create_new_best_combination(&city, &chosen_layouts, &chosen_layouts, db, &mut cache, false, print_progress) {
+        if create_new_best_combination(&city, &chosen_layouts, &chosen_layouts, db, &mut cache, &right_distances, false, print_progress) {
             last_improve_step = LastStep::Vertical;
         }
         if print_progress { eprintln!("Finished vertical cuts, improvement: {}", last_improve_step == LastStep::Vertical); }
@@ -77,7 +83,7 @@ pub fn iterate_combines<TDB: LayoutDB>(mut db: &mut TDB, top_layout_count: usize
         let transposed_chosen_layouts: Vec<_> = chosen_layouts.iter().map(|x| transpose_saved_layout(x)).collect();
 
         if print_progress { eprintln!("Starting to combine {} top houses DB; horizontal cuts", top_layout_count); }
-        if create_new_best_combination(&transposed_city, &transposed_chosen_layouts, &transposed_chosen_layouts, db, &mut cache, true, print_progress) {
+        if create_new_best_combination(&transposed_city, &transposed_chosen_layouts, &transposed_chosen_layouts, db, &mut cache, &right_distances_transposed, true, print_progress) {
             last_improve_step = LastStep::Horizontal;
         }
         if print_progress { eprintln!("Finished horizontal cuts, improvement: {}", last_improve_step == LastStep::Horizontal); }
@@ -108,7 +114,7 @@ fn transpose_saved_layout(layout: &SavedLayout) -> SavedLayout {
     SavedLayout::new(layout.id(), transposed)
 }
 
-pub fn create_new_best_combination<TDB: LayoutDB>(city: &City, left_layouts: &Vec<SavedLayout>, right_layouts: &Vec<SavedLayout>, db: &mut TDB, cache: &mut CompatibilityCache, transposed: bool, print_progress: bool) -> bool {
+pub fn create_new_best_combination<TDB: LayoutDB>(city: &City, left_layouts: &Vec<SavedLayout>, right_layouts: &Vec<SavedLayout>, db: &mut TDB, cache: &mut CompatibilityCache, right_distances: &HouseDistances, transposed: bool, print_progress: bool) -> bool {
     let mut best_price = left_layouts.iter().chain(right_layouts.iter())
         .map(|layout| city::get_price(&city, layout.houses()))
         .min();
@@ -248,7 +254,7 @@ pub fn create_new_best_combination<TDB: LayoutDB>(city: &City, left_layouts: &Ve
             }
             let compatible = match cache.is_compatible(left.layout, right.layout, left.line.last_update_x, right.line.last_update_x, transposed) {
                 None => {
-                    let compatible = is_compatible(city, &left.line, &right.line);
+                    let compatible = is_compatible(city, right_distances, &left.line, &right.line);
                     cache.set_compatible(left.layout, right.layout, left.line.last_update_x, right.line.last_update_x, transposed, compatible);
                     compatible
                 }
@@ -306,14 +312,13 @@ pub fn create_new_best_combination<TDB: LayoutDB>(city: &City, left_layouts: &Ve
     improved
 }
 
-fn is_compatible(city: &City, left: &LeftLine, right: &RightLine) -> bool {
+fn is_compatible(city: &City, right_distances: &HouseDistances, left: &LeftLine, right: &RightLine) -> bool {
     for y in 0..city.height() {
         let max_left_covered_x = left.get_max_covered_x(y);
         let min_right_covered_x = right.get_min_covered_x(y);
 
-        // This range will often be empty
+        if let Some(right_house) = right_distances.get_closest_house_xy(max_left_covered_x, y) {
-        for x in (max_left_covered_x + 1)..min_right_covered_x {
+            if right_house.x < min_right_covered_x {
-            if city.is_house_xy(x, y) {
                 return false;
             }
         }