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@@ -0,0 +1,418 @@
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+#[macro_use]
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+extern crate lazy_static;
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+
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+use std::collections::HashSet;
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+use std::error::Error;
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+use std::fs::File;
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+use std::io::{prelude::*, BufReader};
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+use std::ops::AddAssign;
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+use std::ops::Index;
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+use std::result;
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+use std::str::FromStr;
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+
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+use num::integer::lcm;
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+use regex::Regex;
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+
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+type Result<T> = result::Result<T, Box<dyn Error>>;
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+
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+const INPUT: &str = "input/input.txt";
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+
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+#[derive(Debug, PartialEq, Eq, Clone, Copy, Hash)]
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+struct Vector {
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+ x: i64,
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+ y: i64,
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+ z: i64,
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+}
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+
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+#[derive(Debug, PartialEq, Eq, Hash, Clone)]
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+struct Body {
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+ position: Vector,
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+ velocity: Vector,
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+}
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+
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+#[derive(Debug, PartialEq, Eq, Hash, Clone)]
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+struct NBody {
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+ bodies: Vec<Body>,
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+}
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+
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+impl FromStr for Body {
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+ type Err = Box<dyn Error>;
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+
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+ fn from_str(s: &str) -> Result<Body> {
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+ lazy_static! {
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+ static ref RE: Regex =
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+ Regex::new(r"<x=(?P<x>-?\d+), y=(?P<y>-?\d+), z=(?P<z>-?\d+)>").unwrap();
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+ }
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+
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+ let captures = match RE.captures(s) {
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+ None => {
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+ return Err(From::from("Malformed scan, no positions could be found"));
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+ }
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+ Some(captures) => captures,
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+ };
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+
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+ Ok(Body {
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+ position: Vector {
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+ x: captures["x"].parse()?,
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+ y: captures["y"].parse()?,
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+ z: captures["z"].parse()?,
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+ },
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+ velocity: Vector::new(),
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+ })
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+ }
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+}
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+
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+impl Vector {
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+ fn new() -> Vector {
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+ Vector { x: 0, y: 0, z: 0 }
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+ }
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+}
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+
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+impl AddAssign for Vector {
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+ fn add_assign(&mut self, other: Self) {
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+ *self = Self {
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+ x: self.x + other.x,
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+ y: self.y + other.y,
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+ z: self.z + other.z,
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+ }
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+ }
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+}
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+
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+impl Index<&str> for Vector {
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+ type Output = i64;
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+
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+ fn index(&self, index: &str) -> &i64 {
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+ match index {
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+ "x" => &self.x,
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+ "y" => &self.y,
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+ "z" => &self.z,
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+ _ => panic!("unknown field: {}", index),
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+ }
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+ }
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+}
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+
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+impl Body {
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+ fn add_gravity(&self, gravity: &mut Vector, other: &Self) {
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+ if self.position.x > other.position.x {
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+ gravity.x -= 1;
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+ } else if self.position.x < other.position.x {
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+ gravity.x += 1;
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+ }
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+
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+ if self.position.y > other.position.y {
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+ gravity.y -= 1;
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+ } else if self.position.y < other.position.y {
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+ gravity.y += 1;
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+ }
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+
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+ if self.position.z > other.position.z {
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+ gravity.z -= 1;
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+ } else if self.position.z < other.position.z {
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+ gravity.z += 1;
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+ }
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+ }
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+}
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+
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+impl NBody {
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+ fn run_step(&mut self) {
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+ let mut gravities = Vec::new();
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+ for body in self.bodies.iter() {
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+ let mut gravity = Vector::new();
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+ for other_body in self.bodies.iter() {
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+ body.add_gravity(&mut gravity, other_body);
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+ }
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+ gravities.push(gravity);
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+ }
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+
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+ for (index, gravity) in gravities.into_iter().enumerate() {
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+ self.bodies[index].velocity += gravity;
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+ let velocity = self.bodies[index].velocity;
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+ self.bodies[index].position += velocity;
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+ }
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+ }
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+
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+ fn total_energy(&self) -> i64 {
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+ let mut total_energy = 0;
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+ for body in self.bodies.iter() {
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+ let potential_energy =
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+ body.position.x.abs() + body.position.y.abs() + body.position.z.abs();
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+ let kinetic_energy =
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+ body.velocity.x.abs() + body.velocity.y.abs() + body.velocity.z.abs();
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+ total_energy += potential_energy * kinetic_energy;
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+ }
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+ total_energy
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+ }
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+
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+ fn state(&self, component: &str) -> [(i64, i64); 4] {
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+ [
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+ (
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+ self.bodies[0].position[component],
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+ self.bodies[0].velocity[component],
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+ ),
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+ (
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+ self.bodies[1].position[component],
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+ self.bodies[1].velocity[component],
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+ ),
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+ (
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+ self.bodies[2].position[component],
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+ self.bodies[2].velocity[component],
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+ ),
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+ (
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+ self.bodies[3].position[component],
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+ self.bodies[3].velocity[component],
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+ ),
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+ ]
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+ }
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+}
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+
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+fn read_moon_scan(filename: &str) -> Result<NBody> {
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+ let file = File::open(filename)?;
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+ let reader = BufReader::new(file);
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+ let mut moons = vec![];
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+
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+ for line in reader.lines() {
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+ moons.push(line?.parse()?);
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+ }
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+
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+ Ok(NBody { bodies: moons })
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+}
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+
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+fn solve_part1(filename: &str) -> Result<i64> {
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+ let mut nbody = read_moon_scan(filename)?;
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+ for _ in 0..1000 {
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+ nbody.run_step();
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+ }
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+ Ok(nbody.total_energy())
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+}
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+
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+fn solve_part2(filename: &str) -> Result<u64> {
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+ let mut step_count = 0;
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+ let mut x_states: HashSet<[(i64, i64); 4]> = HashSet::new();
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+ let mut y_states: HashSet<[(i64, i64); 4]> = HashSet::new();
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+ let mut z_states: HashSet<[(i64, i64); 4]> = HashSet::new();
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+ let mut x_repeated_step_count = None;
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+ let mut y_repeated_step_count = None;
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+ let mut z_repeated_step_count = None;
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+ let mut nbody = read_moon_scan(filename)?;
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+ while x_repeated_step_count == None
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+ || y_repeated_step_count == None
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+ || z_repeated_step_count == None
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+ {
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+ if x_repeated_step_count == None {
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+ let x_state = nbody.state("x");
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+ if x_states.contains(&x_state) {
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+ x_repeated_step_count = Some(step_count);
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+ } else {
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+ x_states.insert(x_state);
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+ }
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+ }
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+
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+ if y_repeated_step_count == None {
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+ let y_state = nbody.state("y");
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+ if y_states.contains(&y_state) {
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+ y_repeated_step_count = Some(step_count);
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+ } else {
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+ y_states.insert(y_state);
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+ }
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+ }
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+
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+ if z_repeated_step_count == None {
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+ let z_state = nbody.state("z");
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+ if z_states.contains(&z_state) {
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+ z_repeated_step_count = Some(step_count);
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+ } else {
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+ z_states.insert(z_state);
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+ }
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+ }
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+
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+ nbody.run_step();
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+ step_count += 1;
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+ }
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+
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+ Ok(lcm(
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+ x_repeated_step_count.unwrap(),
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+ lcm(
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+ y_repeated_step_count.unwrap(),
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+ z_repeated_step_count.unwrap(),
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+ ),
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+ ))
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+}
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+
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+fn main() -> Result<()> {
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+ println!("Part 1: {}", solve_part1(INPUT)?);
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+ println!("Part 2: {}", solve_part2(INPUT)?);
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+
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+ Ok(())
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+}
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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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+
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+ const TEST_INPUT1: &str = "input/test1.txt";
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+ const TEST_INPUT2: &str = "input/test2.txt";
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+ fn nbody_1() -> NBody {
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+ NBody {
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+ bodies: vec![
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+ Body {
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+ position: Vector { x: -1, y: 0, z: 2 },
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+ velocity: Vector { x: 0, y: 0, z: 0 },
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+ },
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+ Body {
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+ position: Vector {
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+ x: 2,
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+ y: -10,
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+ z: -7,
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+ },
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+ velocity: Vector { x: 0, y: 0, z: 0 },
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+ },
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+ Body {
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+ position: Vector { x: 4, y: -8, z: 8 },
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+ velocity: Vector { x: 0, y: 0, z: 0 },
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+ },
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+ Body {
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+ position: Vector { x: 3, y: 5, z: -1 },
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+ velocity: Vector { x: 0, y: 0, z: 0 },
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+ },
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+ ],
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+ }
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+ }
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+ fn nbody_1_after_10_steps() -> NBody {
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+ NBody {
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+ bodies: vec![
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+ Body {
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+ position: Vector { x: 2, y: 1, z: -3 },
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+ velocity: Vector { x: -3, y: -2, z: 1 },
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+ },
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+ Body {
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+ position: Vector { x: 1, y: -8, z: 0 },
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+ velocity: Vector { x: -1, y: 1, z: 3 },
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+ },
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+ Body {
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+ position: Vector { x: 3, y: -6, z: 1 },
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+ velocity: Vector { x: 3, y: 2, z: -3 },
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+ },
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+ Body {
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+ position: Vector { x: 2, y: 0, z: 4 },
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+ velocity: Vector { x: 1, y: -1, z: -1 },
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+ },
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+ ],
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+ }
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+ }
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+ fn nbody_2() -> NBody {
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+ NBody {
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+ bodies: vec![
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+ Body {
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+ position: Vector {
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+ x: -8,
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+ y: -10,
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+ z: 0,
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+ },
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+ velocity: Vector { x: 0, y: 0, z: 0 },
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+ },
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+ Body {
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+ position: Vector { x: 5, y: 5, z: 10 },
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+ velocity: Vector { x: 0, y: 0, z: 0 },
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+ },
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+ Body {
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+ position: Vector { x: 2, y: -7, z: 3 },
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+ velocity: Vector { x: 0, y: 0, z: 0 },
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+ },
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+ Body {
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+ position: Vector { x: 9, y: -8, z: -3 },
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+ velocity: Vector { x: 0, y: 0, z: 0 },
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+ },
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+ ],
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+ }
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+ }
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+ fn nbody_2_after_100_steps() -> NBody {
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+ NBody {
|
|
|
330
|
+ bodies: vec![
|
|
|
331
|
+ Body {
|
|
|
332
|
+ position: Vector {
|
|
|
333
|
+ x: 8,
|
|
|
334
|
+ y: -12,
|
|
|
335
|
+ z: -9,
|
|
|
336
|
+ },
|
|
|
337
|
+ velocity: Vector { x: -7, y: 3, z: 0 },
|
|
|
338
|
+ },
|
|
|
339
|
+ Body {
|
|
|
340
|
+ position: Vector {
|
|
|
341
|
+ x: 13,
|
|
|
342
|
+ y: 16,
|
|
|
343
|
+ z: -3,
|
|
|
344
|
+ },
|
|
|
345
|
+ velocity: Vector {
|
|
|
346
|
+ x: 3,
|
|
|
347
|
+ y: -11,
|
|
|
348
|
+ z: -5,
|
|
|
349
|
+ },
|
|
|
350
|
+ },
|
|
|
351
|
+ Body {
|
|
|
352
|
+ position: Vector {
|
|
|
353
|
+ x: -29,
|
|
|
354
|
+ y: -11,
|
|
|
355
|
+ z: -1,
|
|
|
356
|
+ },
|
|
|
357
|
+ velocity: Vector { x: -3, y: 7, z: 4 },
|
|
|
358
|
+ },
|
|
|
359
|
+ Body {
|
|
|
360
|
+ position: Vector {
|
|
|
361
|
+ x: 16,
|
|
|
362
|
+ y: -13,
|
|
|
363
|
+ z: 23,
|
|
|
364
|
+ },
|
|
|
365
|
+ velocity: Vector { x: 7, y: 1, z: 1 },
|
|
|
366
|
+ },
|
|
|
367
|
+ ],
|
|
|
368
|
+ }
|
|
|
369
|
+ }
|
|
|
370
|
+
|
|
|
371
|
+ #[test]
|
|
|
372
|
+ fn reads_moon_scan_file() {
|
|
|
373
|
+ assert_eq!(read_moon_scan(TEST_INPUT1).unwrap(), nbody_1());
|
|
|
374
|
+ assert_eq!(read_moon_scan(TEST_INPUT2).unwrap(), nbody_2());
|
|
|
375
|
+ }
|
|
|
376
|
+
|
|
|
377
|
+ #[test]
|
|
|
378
|
+ fn runs_10_steps() {
|
|
|
379
|
+ let mut nbody = read_moon_scan(TEST_INPUT1).unwrap();
|
|
|
380
|
+ for _ in 0..10 {
|
|
|
381
|
+ nbody.run_step();
|
|
|
382
|
+ }
|
|
|
383
|
+ assert_eq!(nbody, nbody_1_after_10_steps());
|
|
|
384
|
+ }
|
|
|
385
|
+
|
|
|
386
|
+ #[test]
|
|
|
387
|
+ fn runs_100_steps() {
|
|
|
388
|
+ let mut nbody = read_moon_scan(TEST_INPUT2).unwrap();
|
|
|
389
|
+ for _ in 0..100 {
|
|
|
390
|
+ nbody.run_step();
|
|
|
391
|
+ }
|
|
|
392
|
+ assert_eq!(nbody, nbody_2_after_100_steps());
|
|
|
393
|
+ }
|
|
|
394
|
+
|
|
|
395
|
+ #[test]
|
|
|
396
|
+ fn calculates_total_energy_after_10_steps() {
|
|
|
397
|
+ let mut nbody = read_moon_scan(TEST_INPUT1).unwrap();
|
|
|
398
|
+ for _ in 0..10 {
|
|
|
399
|
+ nbody.run_step();
|
|
|
400
|
+ }
|
|
|
401
|
+ assert_eq!(nbody.total_energy(), 179);
|
|
|
402
|
+ }
|
|
|
403
|
+
|
|
|
404
|
+ #[test]
|
|
|
405
|
+ fn calculates_total_energy_after_100_steps() {
|
|
|
406
|
+ let mut nbody = read_moon_scan(TEST_INPUT2).unwrap();
|
|
|
407
|
+ for _ in 0..100 {
|
|
|
408
|
+ nbody.run_step();
|
|
|
409
|
+ }
|
|
|
410
|
+ assert_eq!(nbody.total_energy(), 1940);
|
|
|
411
|
+ }
|
|
|
412
|
+
|
|
|
413
|
+ #[test]
|
|
|
414
|
+ fn finds_repeated_states() {
|
|
|
415
|
+ assert_eq!(solve_part2(TEST_INPUT1).unwrap(), 2772);
|
|
|
416
|
+ assert_eq!(solve_part2(TEST_INPUT2).unwrap(), 4686774924);
|
|
|
417
|
+ }
|
|
|
418
|
+}
|
