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#![allow(dead_code)]
#![allow(unused_variables)]
use advent_of_code::prelude::*;
#[derive(PartialEq, Eq, Clone, Debug)]
pub enum Packet {
Int(usize),
List(Vec<Packet>),
}
impl PartialOrd for Packet {
fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
Some(self.cmp(other))
}
}
impl Ord for Packet {
fn cmp(&self, other: &Self) -> Ordering {
match self {
Self::Int(left) => match other {
Self::Int(right) => left.cmp(right),
Self::List(right) => {
Self::List(vec![self.clone()]).cmp(other)
}
},
Self::List(left) => match other {
Self::Int(right) => {
self.cmp(&Self::List(vec![other.clone()]))
}
Self::List(right) => left.cmp(right),
},
}
}
}
impl Packet {
fn parse(s: &str) -> Result<(Self, &str)> {
if let Some(mut s) = s.strip_prefix('[') {
let mut l = vec![];
while !s.starts_with([',', ']']) {
let (packet, next) = Self::parse(s)?;
l.push(packet);
match next.as_bytes()[0] {
b',' => s = &next[1..],
b']' => {
s = next;
break;
}
_ => bail!("failed to parse"),
}
}
Ok((Self::List(l), &s[1..]))
} else {
let end = s.find([',', ']']).unwrap_or(s.len());
Ok((Self::Int(s[..end].parse()?), &s[end..]))
}
}
}
impl std::str::FromStr for Packet {
type Err = anyhow::Error;
fn from_str(s: &str) -> Result<Self, Self::Err> {
let (packet, rest) = Packet::parse(s)?;
if !rest.is_empty() {
bail!("trailing data: '{}'", rest);
}
Ok(packet)
}
}
pub fn parse(fh: File) -> Result<Vec<(Packet, Packet)>> {
let mut lines = parse::raw_lines(fh);
let mut pairs = vec![];
loop {
let packet1 = lines.next().unwrap();
let packet2 = lines.next().unwrap();
pairs.push((packet1.parse()?, packet2.parse()?));
if let Some(line) = lines.next() {
assert_eq!(line, "");
} else {
break;
}
}
Ok(pairs)
}
pub fn part1(pairs: Vec<(Packet, Packet)>) -> Result<usize> {
let mut total = 0;
for (i, (left, right)) in pairs.iter().enumerate() {
if left <= right {
total += i + 1;
}
}
Ok(total)
}
pub fn part2(pairs: Vec<(Packet, Packet)>) -> Result<usize> {
let div_a = Packet::List(vec![Packet::List(vec![Packet::Int(2)])]);
let div_b = Packet::List(vec![Packet::List(vec![Packet::Int(6)])]);
let mut packets: Vec<Packet> = pairs
.into_iter()
.flat_map(|(left, right)| {
std::iter::once(left).chain(std::iter::once(right))
})
.chain(std::iter::once(div_a.clone()))
.chain(std::iter::once(div_b.clone()))
.collect();
packets.sort_unstable();
let idx_a =
packets.iter().position(|packet| packet == &div_a).unwrap() + 1;
let idx_b =
packets.iter().position(|packet| packet == &div_b).unwrap() + 1;
Ok(idx_a * idx_b)
}
#[test]
fn test() {
assert_eq!(
part1(parse(parse::data(2022, 13).unwrap()).unwrap()).unwrap(),
6070
);
assert_eq!(
part2(parse(parse::data(2022, 13).unwrap()).unwrap()).unwrap(),
20758
);
}
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