Year 2024 Day 8

Author: maneatingape

README.md

@@ -79,6 +79,7 @@ Performance is reasonable even on older hardware, for example a 2011 MacBook Pro
 | 5 | [Print Queue](https://adventofcode.com/2024/day/5) | [Source](src/year2024/day05.rs) | 18 |
 | 6 | [Guard Gallivant](https://adventofcode.com/2024/day/6) | [Source](src/year2024/day06.rs) | 386 |
 | 7 | [Bridge Repair](https://adventofcode.com/2024/day/7) | [Source](src/year2024/day07.rs) | 136 |
+| 8 | [Resonant Collinearity](https://adventofcode.com/2024/day/8) | [Source](src/year2024/day08.rs) | 8 |
 
 ## 2023
 

benches/benchmark.rs

@@ -299,4 +299,5 @@ mod year2024 {
     benchmark!(year2024, day05);
     benchmark!(year2024, day06);
     benchmark!(year2024, day07);
+    benchmark!(year2024, day08);
 }

src/lib.rs

@@ -298,4 +298,5 @@ pub mod year2024 {
     pub mod day05;
     pub mod day06;
     pub mod day07;
+    pub mod day08;
 }

src/main.rs

@@ -368,5 +368,6 @@ fn year2024() -> Vec<Solution> {
         solution!(year2024, day05),
         solution!(year2024, day06),
         solution!(year2024, day07),
+        solution!(year2024, day08),
     ]
 }

src/year2024/day08.rs

@@ -0,0 +1,69 @@
+//! # Resonant Collinearity
+use crate::util::grid::*;
+use crate::util::hash::*;
+use crate::util::point::*;
+
+type Input = (Grid<u8>, FastMap<u8, Vec<Point>>);
+
+pub fn parse(input: &str) -> Input {
+    let grid = Grid::parse(input);
+    let mut antennas = FastMap::new();
+
+    for y in 0..grid.height {
+        for x in 0..grid.width {
+            let point = Point::new(x, y);
+            let frequency = grid[point];
+
+            if frequency != b'.' {
+                antennas.entry(frequency).or_insert_with(Vec::new).push(point);
+            }
+        }
+    }
+
+    (grid, antennas)
+}
+
+pub fn part1(input: &Input) -> u32 {
+    let (grid, antennas) = input;
+    let mut locations = grid.same_size_with(0);
+
+    for frequency in antennas.values() {
+        for &first in frequency {
+            for &second in frequency {
+                if first != second {
+                    let distance = second - first;
+                    let antinode = second + distance;
+
+                    if grid.contains(antinode) {
+                        locations[antinode] = 1;
+                    }
+                }
+            }
+        }
+    }
+
+    locations.bytes.iter().sum()
+}
+
+pub fn part2(input: &Input) -> u32 {
+    let (grid, antennas) = input;
+    let mut locations = grid.same_size_with(0);
+
+    for frequency in antennas.values() {
+        for &first in frequency {
+            for &second in frequency {
+                if first != second {
+                    let distance = second - first;
+                    let mut antinode = second;
+
+                    while grid.contains(antinode) {
+                        locations[antinode] = 1;
+                        antinode += distance;
+                    }
+                }
+            }
+        }
+    }
+
+    locations.bytes.iter().sum()
+}

tests/test.rs

@@ -288,4 +288,5 @@ mod year2024 {
     mod day05_test;
     mod day06_test;
     mod day07_test;
+    mod day08_test;
 }

tests/year2024/day08_test.rs

@@ -0,0 +1,27 @@
+use aoc::year2024::day08::*;
+
+const EXAMPLE: &str = "\
+............
+........0...
+.....0......
+.......0....
+....0.......
+......A.....
+............
+............
+........A...
+.........A..
+............
+............";
+
+#[test]
+fn part1_test() {
+    let input = parse(EXAMPLE);
+    assert_eq!(part1(&input), 14);
+}
+
+#[test]
+fn part2_test() {
+    let input = parse(EXAMPLE);
+    assert_eq!(part2(&input), 34);
+}