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extern crate num;
use std::cmp;
use std::collections::HashMap;
use num::integer;
#[derive(Debug, PartialEq, Eq, Hash, Clone)]
struct Moon {
pos: i64,
vel: i64
}
fn sign(x: i64) -> i64 {
if x < 0 {
-1
} else if x > 0 {
1
} else {
0
}
}
impl Moon {
fn new(pos: i64) -> Moon {
Moon { pos: pos, vel: 0 }
}
fn step(&self, moons: &[Moon]) -> Moon {
let mut vel = self.vel;
for moon in moons {
vel += sign(moon.pos - self.pos);
}
Moon { pos: self.pos + vel, vel: vel }
}
}
#[derive(Debug, PartialEq, Eq, Hash, Clone)]
struct Moons(Vec<Moon>);
impl Moons {
fn step(&self) -> Moons {
Moons(self.0.iter().map(|m| m.step(&self.0)).collect())
}
}
fn run_steps(mut m: Moons, steps: i64, debug: bool) {
for i in 0..steps {
if debug {
println!("After {} steps:", i);
println!("{:?}", m);
}
m = m.step()
}
println!("After {} steps:", steps);
println!("{:?}", m);
}
#[derive(Debug)]
struct Cycle {
start: i64,
length: i64,
moons: Moons,
}
fn find_cycle(mut moons: Moons, limit: i64) -> Option<Cycle> {
let mut m : HashMap<Moons, i64> = HashMap::new();
for i in 0..limit {
if m.contains_key(&moons) {
let start = m[&moons];
return Some(Cycle { start: start, length: i - start, moons: moons.clone() });
} else {
m.insert(moons.clone(), i);
moons = moons.step();
}
}
println!("Giving up after {} steps", limit);
None
}
fn main() {
let moon_x = Moons(vec!(-8, 5, 2, 9).into_iter().map(Moon::new).collect());
let moon_y = Moons(vec!(-10, 5, -7, -8).into_iter().map(Moon::new).collect());
let moon_z = Moons(vec!(0, 10, 3, -3).into_iter().map(Moon::new).collect());
let cycle_x = find_cycle(moon_x, 1 << 30);
let cycle_y = find_cycle(moon_y, 1 << 30);
let cycle_z = find_cycle(moon_z, 1 << 30);
if let (Some(cx), Some(cy), Some(cz)) = (cycle_x, cycle_y, cycle_z) {
println!("cycles:\n{:?}\n{:?}\n{:?}", cx, cy, cz);
let start = cmp::max(cx.start, cmp::max(cy.start, cz.start));
let length = integer::lcm(cx.length, integer::lcm(cy.length, cz.length));
println!("common cycle: start={} length={}", start, length);
} else {
println!("failed");
}
}
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