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main.rs
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main.rs
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#[macro_use]
extern crate lazy_static;
extern crate regex;
use std::collections::{HashMap, HashSet};
use std::error::Error;
use std::io::{self, Read, Write};
use std::result;
use std::str::FromStr;
use regex::Regex;
macro_rules! err {
($($tt:tt)*) => { Err(Box::<Error>::from(format!($($tt)*))) }
}
type Result<T> = result::Result<T, Box<Error>>;
/// A map from step to all of its required dependency steps. The set of
/// required dependency sets may be empty.
type RequiredFor = HashMap<Step, HashSet<Step>>;
type Step = char;
fn main() -> Result<()> {
let mut input = String::new();
io::stdin().read_to_string(&mut input)?;
let mut deps: Vec<Dependency> = vec![];
for line in input.lines() {
let dep = line.parse().or_else(|err| {
err!("failed to parse '{:?}': {}", line, err)
})?;
deps.push(dep);
}
let mut required_for: RequiredFor = HashMap::new();
for dep in deps {
required_for.entry(dep.step).or_default().insert(dep.required);
required_for.entry(dep.required).or_default();
}
part1(&required_for)?;
part2(&required_for)?;
Ok(())
}
fn part1(required_for: &RequiredFor) -> Result<()> {
let mut taken: HashSet<Step> = HashSet::new();
let mut order: Vec<Step> = vec![];
let mut next: Vec<Step> = vec![];
loop {
find_next_steps(&required_for, &taken, &taken, &mut next);
let next_step = match next.pop() {
None => break,
Some(next_step) => next_step,
};
taken.insert(next_step);
order.push(next_step);
}
let answer: String = order.iter().cloned().collect();
writeln!(io::stdout(), "step order: {}", answer)?;
Ok(())
}
fn part2(required_for: &RequiredFor) -> Result<()> {
let mut workers = Workers::new(5);
let mut assigned: HashSet<Step> = HashSet::new();
let mut done: HashSet<Step> = HashSet::new();
let mut order: Vec<Step> = vec![];
let mut next: Vec<Step> = vec![];
let mut seconds = 0;
loop {
workers.run_one_step(&mut order, &mut done);
find_next_steps(&required_for, &assigned, &done, &mut next);
if next.is_empty() && workers.all_idle() {
break;
}
for worker in workers.available() {
let next_step = match next.pop() {
None => break,
Some(next_step) => next_step,
};
assigned.insert(next_step);
workers.work_on(worker, next_step);
}
seconds += 1;
}
let answer: String = order.iter().cloned().collect();
writeln!(io::stdout(), "step order (part 2): {}", answer)?;
writeln!(io::stdout(), "total seconds: {}", seconds)?;
Ok(())
}
/// Populate `next_stack` with next steps such that the steps are sorted in
/// reverse lexicographically with no duplicates.
///
/// Steps in `taken` are never added to the stack.
///
/// Steps in `done` signify which steps have already been completed. Only steps
/// with all dependencies completed will be put on to the stack.
fn find_next_steps(
required_for: &RequiredFor,
taken: &HashSet<Step>,
done: &HashSet<Step>,
next_stack: &mut Vec<Step>,
) {
for (&step, dependencies) in required_for {
if taken.contains(&step) {
continue;
}
if dependencies.iter().all(|s| done.contains(s)) {
next_stack.push(step);
}
}
next_stack.sort();
next_stack.dedup();
next_stack.reverse();
}
/// Workers manages the simulation of a fixed size worker pool. This tracks
/// the status of each worker, whether idle or active. When active, we record
/// how much and what work remains until that worker is idle again.
#[derive(Debug)]
struct Workers {
status: Vec<Status>,
}
type WorkerID = usize;
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
enum Status {
Idle,
Working { step: Step, remaining: u32 }
}
impl Workers {
fn new(count: usize) -> Workers {
Workers { status: vec![Status::Idle; count] }
}
fn available(&self) -> Vec<WorkerID> {
let mut available = vec![];
for (worker, &status) in self.status.iter().enumerate() {
if status == Status::Idle {
available.push(worker);
}
}
available
}
fn all_idle(&self) -> bool {
self.status.iter().all(|s| *s == Status::Idle)
}
fn work_on(&mut self, worker: WorkerID, step: Step) {
let status = &mut self.status[worker];
assert!(*status == Status::Idle, "worker {} is not available", worker);
let remaining = (step as u32) - b'A' as u32 + 1 + 60;
*status = Status::Working { step, remaining }
}
/// Run one step in the simulation. Workers that have finished their work
/// are transitioned to idle status.
fn run_one_step(&mut self, order: &mut Vec<Step>, done: &mut HashSet<Step>) {
for worker in 0..self.status.len() {
let mut is_done = false;
match self.status[worker] {
Status::Idle => {}
Status::Working { step, ref mut remaining } => {
*remaining -= 1;
if *remaining == 0 {
is_done = true;
order.push(step);
done.insert(step);
}
}
}
if is_done {
self.status[worker] = Status::Idle;
}
}
}
}
#[derive(Clone, Copy, Debug)]
struct Dependency {
step: Step,
required: Step,
}
impl FromStr for Dependency {
type Err = Box<Error>;
fn from_str(s: &str) -> Result<Dependency> {
lazy_static! {
static ref RE: Regex = Regex::new(
r"Step ([A-Z]) must be finished before step ([A-Z]) can begin."
).unwrap();
}
let caps = match RE.captures(s) {
None => return err!("unrecognized dependency"),
Some(caps) => caps,
};
Ok(Dependency {
step: caps[2].as_bytes()[0] as Step,
required: caps[1].as_bytes()[0] as Step,
})
}
}