115 lines
3.1 KiB
Rust
115 lines
3.1 KiB
Rust
use std::collections::HashMap;
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use std::io::{self, BufRead};
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#[derive(Clone, Debug)]
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struct Asteroid {
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x: i64,
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y: i64,
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visible_asteroids: HashMap<i64, Vec<Asteroid>>,
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}
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impl Asteroid {
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pub fn new(x: usize, y: usize) -> Self {
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Self {
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x: x as i64,
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y: y as i64,
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visible_asteroids: HashMap::new(),
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}
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}
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fn compute_visibles(mut self, all_asteroids: &[Asteroid]) -> Self {
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for ast in all_asteroids {
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if ast.x == self.x && ast.y == self.y {
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continue;
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}
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let angle = calculate_angle(self.x - ast.x, self.y - ast.y);
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self.visible_asteroids.entry(angle).or_insert_with(Vec::new);
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self.visible_asteroids
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.get_mut(&angle)
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.unwrap()
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.push(ast.to_owned());
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}
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self
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}
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fn fire_mah_laz0r(self, limit: usize) -> Asteroid {
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let x = self.x;
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let y = self.y;
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let mut visibles: Vec<(i64, Vec<Asteroid>)> = self
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.visible_asteroids
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.into_iter()
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.map(|(angle, mut asts)| {
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asts.sort_by_key(|a| -((a.x - x).abs() + (a.y - y).abs()));
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(angle, asts)
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})
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.collect();
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visibles.sort_by_key(|&(angle, _)| angle);
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let mut num_destroyed = 0;
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for (_, mut asts) in visibles.into_iter().cycle() {
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match asts.pop() {
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None => (),
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Some(ast) => {
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num_destroyed += 1;
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if num_destroyed == limit {
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return ast;
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}
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}
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}
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}
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unreachable!()
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}
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}
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fn read_input() -> Vec<Asteroid> {
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io::stdin()
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.lock()
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.lines()
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.enumerate()
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.flat_map(|(y, l)| {
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l.unwrap()
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.chars()
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.enumerate()
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.filter(|(_, c)| c == &'#')
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.map(move |(x, _)| Asteroid::new(x, y))
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.collect::<Vec<_>>()
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})
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.collect()
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}
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fn main() {
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let input = read_input();
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let part1 = input
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.clone()
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.into_iter()
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.map(|ast| ast.compute_visibles(&input))
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.max_by_key(|ast| ast.visible_asteroids.len())
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.unwrap();
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println!("Part 1: {}", part1.visible_asteroids.len());
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let part2 = part1.fire_mah_laz0r(200);
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println!("Part 2: {}", part2.x * 100 + part2.y);
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}
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fn calculate_angle(x_offset: i64, y_offset: i64) -> i64 {
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// Angles in the assignment start at 0 degrees when pointing up (negative y), so we have to
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// offset them here.
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let mut raw_angle =
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(((y_offset as f64).atan2(x_offset as f64).to_degrees() * 1000.0).round() as i64) - 90_000;
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if raw_angle < 0 {
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raw_angle += 360_000;
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}
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raw_angle
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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fn test_angle_calculation() {
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assert_eq!(calculate_angle(0, -1), 0);
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assert_eq!(calculate_angle(1, 0), 90_000);
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assert_eq!(calculate_angle(1, 1), 135_000);
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assert_eq!(calculate_angle(-1, -1), 315_000);
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}
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}
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