2019: Day 10

2019/input_10.txt

@@ -0,0 +1,42 @@
+..............#.#...............#....#....
+#.##.......#....#.#..##........#...#......
+..#.....#....#..#.#....#.....#.#.##..#..#.
+...........##...#...##....#.#.#....#.##..#
+....##....#...........#..#....#......#.###
+.#...#......#.#.#.#...#....#.##.##......##
+#.##....#.....#.....#...####........###...
+.####....#.......#...##..#..#......#...#..
+...............#...........#..#.#.#.......
+........#.........##...#..........#..##...
+...#..................#....#....##..#.....
+.............#..#.#.........#........#.##.
+...#.#....................##..##..........
+.....#.#...##..............#...........#..
+......#..###.#........#.....#.##.#......#.
+#......#.#.....#...........##.#.....#..#.#
+.#.............#..#.....##.....###..#..#..
+.#...#.....#.....##.#......##....##....#..
+.........#.#..##............#..#...#......
+..#..##...#.#..#....#..#.#.......#.##.....
+#.......#.#....#.#..##.#...#.......#..###.
+.#..........#...##.#....#...#.#.........#.
+..#.#.......##..#.##..#.......#.###.......
+...#....###...#......#..#.....####........
+.............#.#..........#....#......#...
+#................#..................#.###.
+..###.........##...##..##.................
+.#.........#.#####..#...##....#...##......
+........#.#...#......#.................##.
+.##.....#..##.##.#....#....#......#.#....#
+.....#...........#.............#.....#....
+........#.##.#...#.###.###....#.#......#..
+..#...#.......###..#...#.##.....###.....#.
+....#.....#..#.....#...#......###...###...
+#..##.###...##.....#.....#....#...###..#..
+........######.#...............#...#.#...#
+...#.....####.##.....##...##..............
+###..#......#...............#......#...#..
+#..#...#.#........#.#.#...#..#....#.#.####
+#..#...#..........##.#.....##........#.#..
+........#....#..###..##....#.#.......##..#
+.................##............#.......#..

2019/src/bin/puzzle_10.rs

@@ -0,0 +1,117 @@
+use std::collections::BinaryHeap;
+use std::collections::HashMap;
+use std::io;
+
+use aoc2019::grid::Point;
+
+#[derive(Ord, PartialOrd, Eq, PartialEq)]
+struct AsteroidMetadata {
+    loc: Point,
+    distance: u32,
+}
+
+fn gcd(mut a: i32, mut b: i32) -> i32 {
+    while b != 0 {
+        let t = b;
+        b = a % b;
+        a = t;
+    }
+
+    a.abs()
+}
+
+fn distances_from(
+    monitoring_station: Point,
+    asteroids: &[Point],
+) -> HashMap<Point, Vec<AsteroidMetadata>> {
+    let mut result: HashMap<Point, Vec<AsteroidMetadata>> = HashMap::new();
+
+    for &a in asteroids {
+        if a == monitoring_station {
+            continue;
+        }
+
+        let delta = a - monitoring_station;
+        let largest_factor = gcd(delta.x, delta.y);
+
+        result
+            .entry(Point {
+                x: delta.x / largest_factor,
+                y: delta.y / largest_factor,
+            })
+            .or_default()
+            .push(AsteroidMetadata {
+                loc: a,
+                distance: monitoring_station.manhattan_distance(a),
+            });
+    }
+
+    result
+}
+
+fn vaporize_until(asteroids: &HashMap<Point, Vec<AsteroidMetadata>>, count: u32) -> Point {
+    let mut visible: HashMap<_, _> = asteroids
+        .iter()
+        .map(|(k, v)| (k, v.iter().collect::<BinaryHeap<&AsteroidMetadata>>()))
+        .collect();
+
+    let mut vaporization_order: Vec<_> = asteroids.keys().collect();
+
+    // XXX: Note these are vectors (i.e., (dx, dy)) of the asteroids relative to the monitoring
+    //      station. We reverse the arguments to atan2() from atan2(dy, dx) to atan2(dx, dy) to
+    //      achieve a 90°CCW rotation and a vertical flip of the coordiante system. Sorting by the
+    //      reversed arguments achieves a CCW sweep. To get a CW sweep, we reverse the order.
+    vaporization_order.sort_by(|a, b| {
+        f64::from(a.x)
+            .atan2(f64::from(a.y))
+            .total_cmp(&f64::from(b.x).atan2(f64::from(b.y)))
+    });
+    vaporization_order.reverse();
+
+    let mut result: Point = Default::default();
+    let mut i = 0;
+    let count = usize::try_from(count).unwrap();
+    while i < count {
+        result = match visible
+            .get_mut(vaporization_order[i % vaporization_order.len()])
+            .unwrap()
+            .pop()
+        {
+            Some(a) => a.loc,
+            None => continue,
+        };
+        i += 1;
+    }
+
+    result
+}
+
+fn main() {
+    // XXX: Note that y-coordinate is from the top, and x-coordinate is from the left.
+    let mut asteroids = vec![];
+    for (y, row) in io::stdin().lines().map(|line| line.unwrap()).enumerate() {
+        for (x, c) in row.chars().enumerate() {
+            if c == '#' {
+                asteroids.push(Point {
+                    x: i32::try_from(x).unwrap(),
+                    y: i32::try_from(y).unwrap(),
+                });
+            }
+        }
+    }
+
+    let dists_from_station = asteroids
+        .iter()
+        .map(|&loc| (loc, distances_from(loc, &asteroids)))
+        .max_by(|a, b| a.1.len().cmp(&b.1.len()))
+        .unwrap()
+        .1;
+
+    println!("Part 1: {}", dists_from_station.len());
+
+    const BETTED_ASTEROID_VAPORIZED: u32 = 200;
+
+    let asteroid = vaporize_until(&dists_from_station, BETTED_ASTEROID_VAPORIZED);
+
+    println!("Part 2: {}", asteroid.x * 100 + asteroid.y);
+}

2019/src/grid.rs

@@ -1,6 +1,7 @@
 use std::ops::Add;
+use std::ops::Sub;
 
-#[derive(Debug, Copy, Clone, Hash, Eq, PartialEq)]
+#[derive(Debug, Default, Copy, Clone, Hash, Eq, PartialEq, Ord, PartialOrd)]
 pub struct Point {
     pub x: i32,
     pub y: i32,
@@ -22,3 +23,14 @@ impl Add for Point {
         }
     }
 }
+
+impl Sub for Point {
+    type Output = Self;
+
+    fn sub(self, other: Self) -> Self {
+        Self {
+            x: self.x - other.x,
+            y: self.y - other.y,
+        }
+    }
+}