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use {
anyhow::{
anyhow,
Context,
Result,
},
regex::Regex,
std::{
collections::HashMap,
env::args,
path::Path,
},
};
type Stack = Vec<char>;
type Stacks = HashMap<usize, Stack>;
#[derive(Debug)]
struct Rearrangment {
count: usize,
from: usize,
to: usize,
}
impl Rearrangment {
fn new(count: usize, from: usize, to: usize) -> Self {
Self {
count,
from,
to,
}
}
}
fn read_input<T: AsRef<Path>>(filename: T) -> Result<(Stacks, Vec<Rearrangment>)> {
let re = Regex::new(r"move (?P<count>[0-9]+) from (?P<from>[0-9]+) to (?P<to>[0-9]+)")?;
let content = std::fs::read_to_string(filename)?;
let (picture, lines) = content.split_once("\n\n").ok_or_else(|| anyhow!("Invalid input"))?;
let mut stacks = HashMap::new();
for layer in picture.split('\n') {
for (num, chunk) in layer.as_bytes().chunks(4).enumerate() {
let byte = chunk.get(1).ok_or_else(|| anyhow!("Could not parse picture."))?;
let ch = *byte as char;
if ('A'..='Z').contains(&ch) {
stacks.entry(num + 1).and_modify(|e: &mut Vec<char>| e.insert(0, ch))
.or_insert_with(|| vec![ch]);
}
}
}
let rearrangements = lines.split('\n').filter(|line| !line.is_empty()).map(|line| {
let caps = re.captures(line).ok_or_else(|| anyhow!("Regex matching failed."))?;
match (caps.name("count"), caps.name("from"), caps.name("to")) {
(Some(count), Some(from), Some(to)) => Ok(Rearrangment::new(count.as_str().parse()?,
from.as_str().parse()?, to.as_str().parse()?)),
_ => Err(anyhow!("Failed to parse rearrangements.")),
}
}).collect::<Result<Vec<_>>>()?;
Ok((stacks, rearrangements))
}
fn part1(input_stacks: &Stacks, rearrangements: &[Rearrangment]) -> Result<String> {
let mut stacks = input_stacks.clone();
for rearrangement in rearrangements {
let count = rearrangement.count;
let from = rearrangement.from;
let to = rearrangement.to;
for _ in 0..count {
let source = stacks.get_mut(&from)
.ok_or_else(|| anyhow!("Missing stack {from}"))?;
if let Some(elem) = source.pop() {
let destination = stacks.get_mut(&to)
.ok_or_else(|| anyhow!("Missing stack {to}"))?;
destination.push(elem);
}
}
}
let mut keys: Vec<_> = stacks.keys().cloned().collect();
keys.sort();
Ok(keys.iter().filter_map(|key| {
let stack = stacks.get_mut(key).unwrap_or_else(|| unreachable!());
stack.pop()
}).collect())
}
fn part2(input_stacks: &Stacks, rearrangements: &[Rearrangment]) -> Result<String> {
let mut stacks = input_stacks.clone();
for rearrangement in rearrangements {
let count = rearrangement.count;
let from = rearrangement.from;
let to = rearrangement.to;
let source = stacks.get_mut(&from)
.ok_or_else(|| anyhow!("Missing stack {from}"))?;
let mut elems = source.drain(source.len()-count..).collect();
let destination = stacks.get_mut(&to)
.ok_or_else(|| anyhow!("Missing stack {to}"))?;
destination.append(&mut elems);
}
let mut keys: Vec<_> = stacks.keys().cloned().collect();
keys.sort();
Ok(keys.iter().filter_map(|key| {
let stack = stacks.get_mut(key).unwrap_or_else(|| unreachable!());
stack.pop()
}).collect())
}
fn main() -> Result<()> {
let ( do_part_1, do_part_2 ) = aoc::do_parts();
let filename = args().nth(1).ok_or_else(|| anyhow!("Missing input filename"))?;
let (stacks, rearrangements) = read_input(filename).context("Could not read input")?;
if do_part_1 {
let solution = part1(&stacks, &rearrangements).context("No solution for part 1")?;
println!("Part1, solution found to be: {}", solution);
}
if do_part_2 {
let solution = part2(&stacks, &rearrangements).context("No solution for part 2")?;
println!("Part2, solution found to be: {}", solution);
}
Ok(())
}
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