diff --git a/src/main.rs b/src/main.rs
index 5753b1c..4fbc846 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -2,6 +2,7 @@ use rand::prelude::{StdRng, SliceRandom};
 use rand::{SeedableRng, Rng, thread_rng};
 use std::fmt;
 use std::fmt::Formatter;
+use std::collections::{HashMap, HashSet};
 
 pub const SIZE: usize = 16384;
 pub const HOUSE_RANGE: usize = 500;
@@ -95,6 +96,20 @@ impl fmt::Display for Rectangle {
     }
 }
 
+impl Rectangle {
+    pub fn is_inside(&self, x: usize, y: usize) -> bool {
+        self.left <= x && x <= self.right && self.top <= y && y <= self.bottom
+    }
+
+    pub fn width(&self) -> usize {
+        self.right - self.left
+    }
+
+    pub fn height(&self) -> usize {
+        self.bottom - self.top
+    }
+}
+
 pub struct HouseLayout<'a> {
     city: &'a City,
     reachable: Vec<u16>,
@@ -166,108 +181,292 @@ impl<'a> HouseLayout<'a> {
     }
 }
 
+fn dump_layout(layout: &HouseLayout, best_price: &mut Option<u32>, seed: u64) {
+    let price = layout.price();
+    if best_price.is_none() || price < best_price.unwrap() {
+        *best_price = Some(price);
+        eprintln!("Printing {} - new best", price);
+        println!("New best!");
+        println!("Price {}, seed {}", price, seed);
+        print_houses(&layout.houses());
+        println!();
+    } else {
+        eprintln!("Printing {}", price);
+        println!("Price {}, seed {}", price, seed);
+        print_houses(&layout.houses());
+        println!();
+    }
+}
+
+
 fn main() {
     let city = City::read_from_file("01.in");
-
     let mut best_price: Option<u32> = None;
+
     loop {
         let seed: u64 = thread_rng().gen();
         eprintln!("Starting seed {}", seed);
-
         let mut rng = StdRng::seed_from_u64(seed);
         let mut layout = HouseLayout::new(&city);
+        eprintln!("Starting random population...");
+        populate_random(&mut layout, &mut rng);
+        eprintln!("Finished random init, price: {}", layout.price());
         loop {
-            loop {
-                let x = rng.gen_range(0..SIZE);
-                let y = rng.gen_range(0..SIZE);
-                let house = House::new(x, y);
-                if city.is_house_xy(x, y) && !layout.is_covered(house) {
-                    layout.add_house(house);
-                    break;
-                }
+            let mut improved = false;
+            eprintln!("Starting moving individual houses...");
+            if improve_move_individual_houses(&mut layout, &mut rng) {
+                dump_layout(&layout, &mut best_price, seed);
+                improved = true;
+            }
+            eprintln!("Finished moving individual houses...");
+            eprintln!("Starting pairwise house merge...");
+            if improve_merge_pairwise(&mut layout) {
+                dump_layout(&layout, &mut best_price, seed);
+                improved = true;
             }
+            eprintln!("Finished pairwise house merge");
+            if !improved {
+                break;
+            }
+        }
+    }
+}
 
-            if layout.is_valid() {
+fn populate_random(layout: &mut HouseLayout, rng: &mut StdRng) {
+    loop {
+        loop {
+            let x = rng.gen_range(0..SIZE);
+            let y = rng.gen_range(0..SIZE);
+            let house = House::new(x, y);
+            if layout.city.is_house_xy(x, y) && !layout.is_covered(house) {
+                layout.add_house(house);
                 break;
             }
         }
 
-        eprintln!("Finished random init, price: {}", layout.price());
+        if layout.is_valid() {
+            break;
+        }
+    }
+}
 
-        let mut untried_houses = layout.houses().clone();
-        untried_houses.shuffle(&mut rng);
-
-        while untried_houses.len() > 0 {
-            let house = untried_houses.pop().unwrap();
-            let mut house_index = layout.houses().iter().position(|x| *x == house).unwrap();
-
-            let move_rectangle = match get_valid_move_rectangle(&layout, house) {
-                Ok(move_rectangle) => move_rectangle,
-                Err(RectangleSearchError::UselessHouse) => {
-                    let old_price = layout.price();
-                    layout.remove_house(house_index);
-                    let new_price = layout.price();
-                    let price_diff = new_price as i64 - old_price as i64;
-                    //eprintln!(" candidate is valid, price diff: {}.", price_diff);
-                    //eprintln!("Removed a house (useless), diff {}", price_diff);
-                    //eprintln!("Improved price: {}", new_price);
-                    untried_houses = layout.houses().clone();
-                    untried_houses.shuffle(&mut rng);
-                    continue;
+fn improve_move_individual_houses(layout: &mut HouseLayout, mut rng: &mut StdRng) -> bool {
+    let mut improved = false;
+    let mut untried_houses = layout.houses().clone();
+    untried_houses.shuffle(&mut rng);
+
+    while untried_houses.len() > 0 {
+        let house = untried_houses.pop().unwrap();
+        let house_index = layout.houses().iter().position(|x| *x == house).unwrap();
+
+        let move_rectangle = match get_valid_move_rectangle(&layout, house) {
+            Ok(move_rectangle) => move_rectangle,
+            Err(RectangleSearchError::Useless) => {
+                //let old_price = layout.price();
+                layout.remove_house(house_index);
+                //let new_price = layout.price();
+                //let price_diff = new_price as i64 - old_price as i64;
+                //eprintln!(" candidate is valid, price diff: {}.", price_diff);
+                //eprintln!("Removed a house (useless), diff {}", price_diff);
+                //eprintln!("Improved price: {}", new_price);
+                improved = true;
+                untried_houses = layout.houses().clone();
+                untried_houses.shuffle(&mut rng);
+                continue;
+            }
+            _ => unreachable!()
+        };
+
+        // TODO: Not needed, can just store best
+        let mut new_candidates = Vec::new();
+        for new_y in move_rectangle.top..=move_rectangle.bottom {
+            for new_x in move_rectangle.left..=move_rectangle.right {
+                if layout.city.is_house_xy(new_x, new_y) && layout.city.get_price_xy(new_x, new_y) < layout.city.get_price(&house) {
+                    new_candidates.push(House::new(new_x, new_y));
                 }
-            };
+            }
+        }
+
+        new_candidates.sort_by(|a, b| layout.city.get_price(&a).cmp(&layout.city.get_price(&b)));
+        if new_candidates.len() == 0 {
+            //eprintln!("Did not find candidate");
+        } else {
+            for (i, &candidate) in new_candidates.iter().enumerate() {
+                //eprint!("Found candidate {}...", i);
+
+                //let old_price = layout.price();
+                layout.remove_house(house_index);
+                layout.add_house(candidate);
+
+                assert!(layout.is_valid());
+                //let new_price = layout.price();
+                //let price_diff = new_price as i64 - old_price as i64;
+                //eprintln!(" candidate is valid, price diff: {}.", price_diff);
+                //eprintln!("Improved price: {}", new_price);
+                improved = true;
+                untried_houses = layout.houses().clone();
+                untried_houses.shuffle(&mut rng);
+                break;
+            }
+        }
+    }
+
+    improved
+}
+
 
-            let mut new_candidates = Vec::new();
-            for new_y in move_rectangle.top..=move_rectangle.bottom {
-                for new_x in move_rectangle.left..=move_rectangle.right {
-                    if city.is_house_xy(new_x, new_y) && city.get_price_xy(new_x, new_y) < city.get_price(&house) {
-                        new_candidates.push(House::new(new_x, new_y));
+pub fn improve_merge_pairwise(layout: &mut HouseLayout) -> bool {
+    let mut improved = false;
+
+    loop {
+        // This here is a hack for being unable to modify the houses while looping through them.
+        // We instead go through the houses repeatedly and remember which pairs we have already
+        // tried by hashing their values because they can and do move throughout the layout Vec
+        // as it's being modified.
+        let mut checked = HashSet::new();
+
+        let mut loop_improved = false;
+        loop {
+            let mut merge = None;
+
+            'outer_houses: for i in 0..layout.houses().len() {
+                for j in i + 1..layout.houses().len() {
+                    let house1 = layout.houses()[i];
+                    let house2 = layout.houses()[j];
+
+                    let x_dist = (house1.x as i32 - house2.x as i32).abs() as usize;
+                    let y_dist = (house1.y as i32 - house2.y as i32).abs() as usize;
+                    if x_dist > 4 * HOUSE_RANGE || y_dist > 4 * HOUSE_RANGE {
+                        // Never close enough to merge
+                        continue;
+                    }
+
+                    if checked.contains(&(house1, house2)) || checked.contains(&(house2, house1)) {
+                        continue;
+                    } else {
+                        checked.insert((house1, house2));
+                    }
+
+                    match get_valid_move_rectangle_multiple(&layout, &vec! {house1, house2}) {
+                        Ok(rect) => {
+                            let mut cheapest = None;
+                            for y in rect.top..=rect.bottom {
+                                for x in rect.left..=rect.right {
+                                    if !layout.city.is_house_xy(x, y) { continue; }
+                                    let price = layout.city.get_price_xy(x, y);
+                                    match cheapest {
+                                        None => cheapest = Some((x, y, price)),
+                                        Some((_, _, cheapest_price)) if price < cheapest_price => cheapest = Some((x, y, price)),
+                                        _ => {}
+                                    };
+                                }
+                            }
+                            if let Some((x, y, price)) = cheapest {
+                                if price >= layout.city.get_price(&house1) + layout.city.get_price(&house2) {
+                                    // Merging not worth
+                                    //eprintln!("Merging not worth!");
+                                } else {
+                                    merge = Some((i, j, House::new(x, y)));
+                                    break 'outer_houses;
+                                }
+                            }
+                        }
+                        Err(RectangleSearchError::Useless) => eprintln!("Found useless pair of houses, not solving!"),
+                        Err(RectangleSearchError::Unsatisfiable) => {}
                     }
                 }
             }
 
-            new_candidates.sort_by(|a, b| city.get_price(&a).cmp(&city.get_price(&b)));
-            if new_candidates.len() == 0 {
-                //eprintln!("Did not find candidate");
+            if let Some((i, j, house)) = merge {
+                let old_price = layout.price();
+                assert!(i < j);
+                layout.remove_house(j);
+                layout.remove_house(i);
+                layout.add_house(house);
+
+                assert!(layout.is_valid());
+                let new_price = layout.price();
+                let price_diff = new_price as i32 - old_price as i32;
+                eprintln!("Merged two houses, new price {}, diff {}", new_price, price_diff);
+                improved = true;
+                loop_improved = true;
             } else {
-                for (i, &candidate) in new_candidates.iter().enumerate() {
-                    //eprint!("Found candidate {}...", i);
-
-                    let old_price = layout.price();
-                    layout.remove_house(house_index);
-                    layout.add_house(candidate);
-
-                    assert!(layout.is_valid());
-                    let new_price = layout.price();
-                    let price_diff = new_price as i64 - old_price as i64;
-                    //eprintln!(" candidate is valid, price diff: {}.", price_diff);
-                    //eprintln!("Improved price: {}", new_price);
-                    untried_houses = layout.houses().clone();
-                    untried_houses.shuffle(&mut rng);
-                    break;
-                }
+                break;
             }
         }
 
-        let price = layout.price();
-        if best_price.is_none() || price < best_price.unwrap() {
-            best_price = Some(price);
-            eprintln!("Finished randomization, price: {}, new best, printing", price);
-            println!("New best!");
-            println!("Price {}, seed {}", price, seed);
-            print_houses(&layout.houses());
-            println!();
-        } else {
-            eprintln!("Finished randomization, price: {}, printing", price);
-            println!("Price {}, seed {}", price, seed);
-            print_houses(&layout.houses());
-            println!();
+        if !loop_improved {
+            break;
         }
     }
+
+    improved
 }
 
+
 pub enum RectangleSearchError {
-    UselessHouse
+    Useless,
+    Unsatisfiable
+}
+
+pub fn get_valid_move_rectangle_multiple(layout: &HouseLayout, houses: &Vec<House>) -> Result<Rectangle, RectangleSearchError> {
+    // This is a generalization of get_valid_move_rectangle, it's basically the same thing,
+    // just with a dynamic rectangles_containing_count
+
+    // We first establish a bounding box for an that has to be covered if all houses are removed.
+    let mut covered_rect: Option<Rectangle> = None;
+    for house in houses {
+        let range_rect = house.range_rectangle();
+        for y in range_rect.top..=range_rect.bottom {
+            for x in range_rect.left..=range_rect.right {
+                // We count how many rectangles of houses contain this xy position.
+                let mut rectangles_containing_count = 0;
+                for house in houses {
+                    let rect = house.range_rectangle();
+                    if rect.is_inside(x, y) {
+                        rectangles_containing_count += 1;
+                    }
+                }
+
+                // If this house is covered by the exact amount of rectangles,
+                // then removing all input houses would uncover this position.
+                // It cannot be less than the rectangle count, and more means there
+                // is another house covering it as well.
+                if layout.cover_count_xy(x, y) == rectangles_containing_count && layout.city.is_house_xy(x, y) {
+                    if let Some(cover) = &mut covered_rect {
+                        cover.left = cover.left.min(x);
+                        cover.right = cover.right.max(x);
+                        cover.top = cover.top.min(y);
+                        cover.bottom = cover.bottom.max(y);
+                    } else {
+                        covered_rect = Some(Rectangle { left: x, right: x, top: y, bottom: y });
+                    }
+                }
+            }
+        }
+    };
+
+    if covered_rect.is_none() {
+        // Unnecessary set of houses.
+        return Err(RectangleSearchError::Useless);
+    }
+
+    let covered_rect = covered_rect.unwrap();
+
+    let height_margin = HOUSE_RANGE as i32 - covered_rect.height() as i32;
+    let width_margin = HOUSE_RANGE as i32 - covered_rect.width() as i32;
+
+    let top = (covered_rect.top as i32 - height_margin).max(0) as usize;
+    let left = (covered_rect.left as i32 - width_margin).max(0) as usize;
+    let bottom = (covered_rect.bottom + height_margin as usize).min(SIZE - 1);
+    let right = (covered_rect.right + width_margin as usize).min(SIZE - 1);
+
+    if top > bottom || left > right {
+        // Unsatisfiable rectangle by one house
+        return Err(RectangleSearchError::Unsatisfiable);
+    }
+
+    Ok(Rectangle { left, right, top, bottom })
 }
 
 pub fn get_valid_move_rectangle(layout: &HouseLayout, house: House) -> Result<Rectangle, RectangleSearchError> {
@@ -292,7 +491,7 @@ pub fn get_valid_move_rectangle(layout: &HouseLayout, house: House) -> Result<Re
     }
 
     if covered_rect.is_none() {
-        return Err(RectangleSearchError::UselessHouse)
+        return Err(RectangleSearchError::Useless)
     }
 
     let covered_rect = covered_rect.unwrap();