Day 8

Author: UnderscoreTud

README.md

@@ -28,9 +28,10 @@ Solutions for [Advent of Code](https://adventofcode.com/) in [Rust](https://www.
 | [Day 4](./src/bin/04.rs) | `560.8µs` | `161.9µs` |
 | [Day 5](./src/bin/05.rs) | `344.6µs` | `323.6µs` |
 | [Day 6](./src/bin/06.rs) | `488.0µs` | `119.9ms` |
-| [Day 7](./src/bin/07.rs) | `64.9µs` | `84.1µs` |
+| [Day 7](./src/bin/07.rs) | `80.3µs` | `113.7µs` |
+| [Day 8](./src/bin/08.rs) | `9.9µs` | `12.2µs` |
 
-**Total: 123.85ms**
+**Total: 123.92ms**
 <!--- benchmarking table --->
 
 ---

data/examples/08.txt

@@ -0,0 +1,12 @@
+............
+........0...
+.....0......
+.......0....
+....0.......
+......A.....
+............
+............
+........A...
+.........A..
+............
+............

src/bin/08.rs

@@ -0,0 +1,105 @@
+use std::collections::HashMap;
+
+advent_of_code::solution!(8);
+
+#[derive(Debug)]
+struct Grid {
+    width: usize,
+    height: usize,
+    antennas: HashMap<char, Vec<(usize, usize)>>
+}
+
+impl Grid {
+    fn parse(input: &str) -> Grid {
+        let mut antennas: HashMap<_, Vec<_>> = HashMap::new();
+        let height = input.lines().enumerate().map(|(y, line)| {
+            line.chars().enumerate().for_each(|(x, char)| {
+                if char.is_ascii_alphanumeric() {
+                    antennas.entry(char).or_default().push((x, y));
+                } 
+            });
+            y
+        }).max().unwrap_or_default() + 1;
+        let width = input.lines().next().unwrap_or_default().len();
+        Grid {
+            width,
+            height,
+            antennas,
+        }
+    }
+
+    fn find_antinodes(&self) -> Vec<bool> {
+        let mut antinodes = vec![false; self.width * self.height];
+        self.antennas.iter().for_each(|(_, positions)| positions.iter().enumerate().for_each(|(index, pos1)| positions.iter().skip(index + 1).for_each(|pos2| {
+            let dx= (pos2.0 as isize - pos1.0 as isize) * 2;
+            let dy= (pos2.1 as isize - pos1.1 as isize) * 2;
+
+            if let (Some(x), Some(y)) = (pos1.0.checked_add_signed(dx), pos1.1.checked_add_signed(dy)) {
+                if let Some(index) = self.xy_to_index((x, y)) { antinodes[index] = true; }
+            };
+
+            if let (Some(x), Some(y)) = (pos2.0.checked_add_signed(-dx), pos2.1.checked_add_signed(-dy)) {
+                if let Some(index) = self.xy_to_index((x, y)) { antinodes[index] = true; }
+            }
+        })));
+        antinodes
+    }
+
+    fn find_antinodes_with_resonance(&self) -> Vec<bool> {
+        let mut antinodes = vec![false; self.width * self.height];
+        self.antennas.iter().for_each(|(_, positions)| positions.iter().enumerate().for_each(|(index, pos1)| positions.iter().skip(index + 1).for_each(|pos2| {
+            let dx = pos2.0 as isize - pos1.0 as isize;
+            let dy = pos2.1 as isize - pos1.1 as isize;
+
+            let mut count = 0;
+            while let (Some(x), Some(y)) = (pos1.0.checked_add_signed(-dx * count), pos1.1.checked_add_signed(-dy * count)) {
+                if let Some(index) = self.xy_to_index((x, y)) { antinodes[index] = true; }
+                else { break };
+                count += 1;
+            };
+
+            count = 0;
+            while let (Some(x), Some(y)) = (pos2.0.checked_add_signed(dx * count), pos2.1.checked_add_signed(dy * count)) {
+                if let Some(index) = self.xy_to_index((x, y)) { antinodes[index] = true; }
+                else { break };
+                count += 1;
+            };
+        })));
+        antinodes
+    }
+
+    fn xy_to_index(&self, pos: (usize, usize)) -> Option<usize> {
+        if (0..self.width).contains(&pos.0) && (0..self.height).contains(&pos.1) {
+            Some(pos.1 * self.width + pos.0)
+        } else {
+            None
+        }
+    }
+}
+
+pub fn part_one(input: &str) -> Option<u32> {
+    let grid = Grid::parse(input);
+    Some(grid.find_antinodes().iter().filter(|x| **x).count() as u32)
+}
+
+pub fn part_two(input: &str) -> Option<u32> {
+    let grid = Grid::parse(input);
+    Some(grid.find_antinodes_with_resonance().iter().filter(|x| **x).count() as u32)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_part_one() {
+        let result = part_one(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, Some(14));
+    }
+
+    #[test]
+    fn test_part_two() {
+        let result = part_two(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, Some(34));
+    }
+}