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use aoc2019::*;
use std::io;
use std::io::prelude::*;
use std::iter::FromIterator;
use std::process;
use structopt::StructOpt;
#[derive(Debug, StructOpt)]
#[structopt(name = "Day 10: Monitoring Station")]
/// Finds the asteroid with the best view of the other asteroids. If
/// an n is provided, then it will print the nth asteroid destroyed by
/// a laser from the asteroid with the best view. Otherwise, it will
/// print the number of asteroids visible.
///
/// Takes a map of asteroids in on stdin.
///
/// See https://adventofcode.com/2019/day/10 for details.
struct Opt {
/// indexed from 0
#[structopt(short = "n")]
n: Option<usize>,
}
fn main() {
let opt = Opt::from_args();
let stdin = io::stdin();
let map: AsteroidMap = stdin
.lock()
.lines()
.map(|l| exit_on_failed_assertion(l, "Error reading input"))
.collect();
match opt.n {
Some(n) => println!("{:?}", map.nth_destroyed_asteroid(n)),
None => println!("{}", map.best_asteroid_line_of_sight_count()),
};
}
fn exit_on_failed_assertion<A, E: std::error::Error>(data: Result<A, E>, message: &str) -> A {
match data {
Ok(data) => data,
Err(e) => {
eprintln!("{}: {}", message, e);
process::exit(1);
}
}
}
#[derive(Debug)]
struct AsteroidMap {
asteroids: Vec<Asteroid>,
}
impl FromIterator<String> for AsteroidMap {
fn from_iter<T: IntoIterator<Item = String>>(iter: T) -> Self {
AsteroidMap {
asteroids: iter
.into_iter()
.enumerate()
.flat_map(move |(y, line)| {
line.chars()
.enumerate()
.map(move |(x, c)| (x, y, c))
.collect::<Vec<_>>()
})
.filter(|(_x, _y, c)| *c == '#')
.map(|(x, y, _x)| Asteroid {
x: x as i32,
y: y as i32,
})
.collect(),
}
}
}
impl AsteroidMap {
fn best_asteroid_line_of_sight_count(&self) -> usize {
self.optimal_view_asteroid()
.map(|a| self.count_visible_from(&a))
.unwrap_or(0)
}
fn nth_destroyed_asteroid(&self, n: usize) -> Option<Asteroid> {
self.optimal_view_asteroid()
.and_then(|source| self.nth_destroyed_asteroid_from(&source, n))
}
fn nth_destroyed_asteroid_from(&self, source: &Asteroid, n: usize) -> Option<Asteroid> {
if self.asteroids.len() - 1 < n {
None
} else if self.count_visible_from(source) >= n {
sort_by_key(
self.asteroids
.iter()
.filter(|b| self.has_line_of_sight(source, b)),
|b| (source.angle_to(b) * 100000.) as i32,
)
.nth(n)
.cloned()
} else {
self.remove_visible_to(source)
.nth_destroyed_asteroid_from(source, n - self.count_visible_from(source))
}
}
fn optimal_view_asteroid(&self) -> Option<Asteroid> {
self.asteroids
.iter()
.max_by_key(|a| self.count_visible_from(a))
.cloned()
}
fn count_visible_from(&self, a: &Asteroid) -> usize {
self.asteroids
.iter()
.filter(|b| a != *b && self.has_line_of_sight(a, b))
.count()
}
fn remove_visible_to(&self, source: &Asteroid) -> AsteroidMap {
AsteroidMap {
asteroids: self
.asteroids
.iter()
.filter(|b| self.has_line_of_sight(source, b))
.cloned()
.collect(),
}
}
fn has_line_of_sight(&self, a: &Asteroid, b: &Asteroid) -> bool {
a != b
&& !self.asteroids.iter().any(|c| {
a != c
&& b != c
&& a.angle_to(b) == a.angle_to(c)
&& a.distance_squared(b) > a.distance_squared(c)
})
}
}
#[derive(Debug, Clone, PartialEq, Eq)]
struct Asteroid {
x: i32,
y: i32,
}
impl Asteroid {
fn angle_to(&self, other: &Asteroid) -> f32 {
((self.x as f32 - other.x as f32).atan2(other.y as f32 - self.y as f32)
+ std::f32::consts::PI)
% (2. * std::f32::consts::PI)
}
fn distance_squared(&self, other: &Asteroid) -> i32 {
(self.x - other.x).pow(2) + (self.y - other.y).pow(2)
}
}
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