Day 18 part 1

src/tasks/day18.rs

@@ -0,0 +1,99 @@
+use std::collections::HashMap;
+
+use itertools::Itertools;
+
+use crate::utils;
+
+pub fn task1() {
+    let input = utils::read_file("input/day18.txt");
+    let initial: HashMap<Pos, char> = input
+        .lines()
+        .enumerate()
+        .flat_map(|(y, line)| {
+            line.chars()
+                .enumerate()
+                .map(|(x, c)| (Pos(x as i32, y as i32), c))
+                .collect_vec()
+        })
+        .collect();
+    let fin = (0..10).fold(initial, |map, _| {
+        printmap(&map);
+        map.keys()
+            .map(|p| {
+                let old = map[p];
+                let new = match old {
+                    '.' => {
+                        if neighbors(&map, *p)
+                            .into_iter()
+                            .filter(|c| *c == '|')
+                            .count()
+                            >= 3
+                        {
+                            '|'
+                        } else {
+                            '.'
+                        }
+                    }
+                    '|' => {
+                        if neighbors(&map, *p)
+                            .into_iter()
+                            .filter(|c| *c == '#')
+                            .count()
+                            >= 3
+                        {
+                            '#'
+                        } else {
+                            '|'
+                        }
+                    }
+                    '#' => {
+                        if neighbors(&map, *p).contains(&'#') && neighbors(&map, *p).contains(&'|')
+                        {
+                            '#'
+                        } else {
+                            '.'
+                        }
+                    }
+                    _ => panic!("unknown type"),
+                };
+                (*p, new)
+            })
+            .collect()
+    });
+    let trees = fin.values().filter(|c| **c == '|').count();
+    let lumberyards = fin.values().filter(|c| **c == '#').count();
+    println!("Part 1 - {trees} x {lumberyards} = {}", trees * lumberyards);
+}
+
+fn printmap(map: &HashMap<Pos, char>) {
+    println!();
+    let (x_min, x_max) = map.keys().map(|p| p.0).minmax().into_option().unwrap();
+    let (_y_min, y_max) = map.keys().map(|p| p.1).minmax().into_option().unwrap();
+
+    for y in 0..=y_max {
+        for x in x_min..=x_max {
+            let s = map[&Pos(x, y)];
+            print!("{s}");
+        }
+        print!("\n");
+    }
+}
+
+#[derive(Hash, Eq, PartialEq, Clone, Copy)]
+struct Pos(i32, i32);
+
+fn neighbors(map: &HashMap<Pos, char>, p: Pos) -> Vec<char> {
+    [
+        Pos(p.0 - 1, p.1 - 1),
+        Pos(p.0 - 1, p.1),
+        Pos(p.0 - 1, p.1 + 1),
+        Pos(p.0, p.1 - 1),
+        Pos(p.0, p.1 + 1),
+        Pos(p.0 + 1, p.1 - 1),
+        Pos(p.0 + 1, p.1),
+        Pos(p.0 + 1, p.1 + 1),
+    ]
+    .into_iter()
+    .flat_map(|pos| map.get(&pos).map(|c| *c))
+    .collect_vec()
+}

src/tasks/mod.rs

@@ -14,6 +14,7 @@ pub mod day13;
 pub mod day14;
 pub mod day15;
 pub mod day17;
+pub mod day18;
 pub mod day20;
 pub mod day22;
 pub mod day23;