Day 8

src/day8.rs

@@ -0,0 +1,64 @@
+use std::collections::{HashMap, HashSet};
+
+use itertools::Itertools;
+
+use crate::get_lines;
+
+type Cords = (isize, isize);
+
+#[allow(clippy::cast_possible_wrap)]
+fn parse_field() -> (Cords, HashMap<char, Vec<Cords>>) {
+    let mut positions: HashMap<char, Vec<Cords>> = HashMap::new();
+    let mut dimentions = (0, 0);
+    for (i, line) in get_lines("input.txt").enumerate() {
+        dimentions = (dimentions.0 + 1, dimentions.1.max(line.len() as isize));
+        for (j, c) in line.chars().enumerate() {
+            if c == '.' || c == '#' {
+                continue;
+            }
+            positions
+                .entry(c)
+                .or_default()
+                .push((i as isize, j as isize));
+        }
+    }
+    (dimentions, positions)
+}
+
+#[allow(dead_code)]
+pub fn task1() {
+    let (dimentions, positions) = parse_field();
+    let mut affected: HashSet<Cords> = HashSet::new();
+    for pos in positions.into_values() {
+        for vals in pos.iter().copied().permutations(2) {
+            let [(y1, x1), (y2, x2)] = *vals.as_slice() else {
+                panic!()
+            };
+            let (x3, y3) = (x2 * 2 - x1, y2 * 2 - y1);
+            if (0..dimentions.0).contains(&y3) && (0..dimentions.1).contains(&x3) {
+                affected.insert((y3, x3));
+            }
+        }
+    }
+    println!("{}", affected.len());
+}
+
+#[allow(dead_code)]
+pub fn task2() {
+    let (dimentions, positions) = parse_field();
+    let mut affected: HashSet<Cords> = HashSet::new();
+    for pos in positions.into_values() {
+        for vals in pos.iter().copied().permutations(2) {
+            let [(y1, x1), (mut y2, mut x2)] = *vals.as_slice() else {
+                panic!()
+            };
+            let (dx, dy) = (x2 - x1, y2 - y1);
+            while (0..dimentions.0).contains(&y2) && (0..dimentions.1).contains(&x2) {
+                affected.insert((y2, x2));
+                x2 += dx;
+                y2 += dy;
+            }
+        }
+    }
+    println!("{}", affected.len());
+}

src/main.rs

@@ -5,6 +5,7 @@ mod day4;
 mod day5;
 mod day6;
 mod day7;
+mod day8;
 
 use std::{
     fs::File,
@@ -22,6 +23,6 @@ fn parse_line(line: &str, pattern: char) -> impl Iterator<Item = i32> + '_ {
 }
 
 fn main() {
-    day7::task1();
+    day8::task1();
-    day7::task2();
+    day8::task2();
 }