day19 part 2

src/tasks/day19.rs

@@ -1,24 +1,75 @@
+use std::collections::HashMap;
 use super::day05::{IntCodeComputer, RAM};
 use itertools::Itertools;
 
 pub fn run() {
     let program = super::day05::load_ram("input/day19.txt");
-    part1(program, 50);
+    //part1(&program, 50);
+    part2(&program); // 8151016 too high
 }
 
-fn part1(program: RAM, max: i128) {
+fn part1(program: &RAM, max: i128) {
     let result = (0..max)
         .flat_map(|x| {
             (0..max)
                 .map(|y| {
-                    let mut computer = IntCodeComputer::new(vec![x, y], program.clone());
-                    computer.run_until_end();
-                    *computer.get_output().first().unwrap()
+                    read_coordinate(program, x, y)
                 })
                 .collect_vec()
         })
-        .filter(|v| *v == 1)
+        .filter(|v| *v)
         .count();
 
     println!("{result}");
 }
+
+const W: i128 = 100;
+const MAX_PERIMETER: i128 = 1_000_000_000;
+
+fn part2(program: &RAM) {
+    let mut map: HashMap<(i128, i128), bool> = HashMap::new();
+    (0..W)
+        .for_each(|x| {
+            (0..W)
+                .for_each(|y| {
+                    map.insert((x, y), read_coordinate(program, x, y));
+                })
+        });
+    for starts in 0..=MAX_PERIMETER {
+        println!("checking perimeter {starts}");
+        extend_horizon(program, &mut map, starts);
+        check_all_squares_at(&map, starts);
+    }
+}
+
+fn check_all_squares_at(map: &HashMap<(i128, i128), bool>, starts: i128) {
+    (0..=starts).for_each(|i| {
+        check_fits(map, i, starts);
+        check_fits(map, starts, i);
+    });
+}
+
+fn check_fits(map: &HashMap<(i128, i128), bool>, x: i128, y: i128) {
+    let ul = map[&(x, y)];
+    let ur = map[&(x + W - 1, y)];
+    let ll = map[&(x, y + W - 1)];
+    let lr = map[&(x + W, y + W - 1)];
+    if ul && ur && ll && lr {
+        let result = x * 10_000 + y;
+        panic!("found it! starts at {x},{y} -> {}", result);
+    }
+}
+
+fn extend_horizon(program: &RAM, map: &mut HashMap<(i128, i128), bool>, starts: i128) {
+    (0..=W + starts).for_each(|i| {
+        let j = W + starts;
+        map.insert((j, i), read_coordinate(program, j, i));
+        map.insert((i, j), read_coordinate(program, i, j));
+    });
+}
+
+fn read_coordinate(program: &RAM, x: i128, y: i128) -> bool {
+    let mut computer = IntCodeComputer::new(vec![x, y], program.clone());
+    computer.run_until_end();
+    *computer.get_output().first().unwrap() == 1
+}