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|
mod utils;
use std::{
cmp::Ordering,
iter::{once, Peekable},
};
extern crate nom;
use nom::{bytes::complete::tag, character::complete::u32};
use utils::read_input;
fn main() {
let input = read_input();
let mut full: Vec<_> = input.lines().filter(|x| !x.is_empty()).collect();
println!(
"Part 1: {}",
full.iter()
.step_by(2)
.zip(full.iter().skip(1).step_by(2))
.map(|(left, right)| { compare(left, right) })
.enumerate()
.filter_map(|(i, cmp)| match cmp {
Ordering::Greater => None,
_ => Some(i + 1),
})
.sum::<usize>()
);
full.sort_by(|l, r| compare(l, r));
println!(
"Part 2: {}",
full.iter()
.enumerate()
.filter_map(|(i, val)| match *val {
"[[2]]" | "[[6]]" => Some(i + 1),
_ => None,
})
.product::<usize>()
);
}
fn compare(left: &str, right: &str) -> Ordering {
let mut left = Packet(left).peekable();
let mut right = Packet(right).peekable();
assert_eq!(left.next(), Some(PacketContents::StartList));
assert_eq!(right.next(), Some(PacketContents::StartList));
compare_lists(&mut left, &mut right)
}
fn compare_lists(
left: &mut Peekable<impl Iterator<Item = PacketContents>>,
right: &mut Peekable<impl Iterator<Item = PacketContents>>,
) -> Ordering {
loop {
match (left.next().unwrap(), right.next().unwrap()) {
(PacketContents::EndList, PacketContents::EndList) => {
return Ordering::Equal;
}
(PacketContents::EndList, _) => {
while !matches!(right.next(), Some(PacketContents::EndList)) {}
return Ordering::Less;
}
(_, PacketContents::EndList) => {
while !matches!(left.next(), Some(PacketContents::EndList)) {}
return Ordering::Greater;
}
(PacketContents::StartList, PacketContents::StartList) => {
match compare_lists(left, right) {
Ordering::Equal => (),
x => return x,
}
}
(l @ PacketContents::Integer(_), PacketContents::StartList) => {
match compare_lists(
&mut once(l).chain(once(PacketContents::EndList)).peekable(),
right,
) {
Ordering::Equal => (),
x => return x,
}
}
(PacketContents::StartList, r @ PacketContents::Integer(_)) => {
match compare_lists(
left,
&mut once(r).chain(once(PacketContents::EndList)).peekable(),
) {
Ordering::Equal => (),
x => return x,
}
}
(PacketContents::Integer(l), PacketContents::Integer(r)) => match l.cmp(&r) {
Ordering::Equal => (),
x => return x,
},
};
}
}
#[derive(Debug, PartialEq, Eq)]
enum PacketContents {
Integer(usize),
StartList,
EndList,
}
struct Packet<'a>(&'a str);
impl Iterator for Packet<'_> {
type Item = PacketContents;
fn next(&mut self) -> Option<Self::Item> {
loop {
if let Ok((i, _)) = tag::<_, _, (&str, nom::error::ErrorKind)>("[")(self.0) {
self.0 = i;
return Some(PacketContents::StartList);
} else if let Ok((i, _)) = tag::<_, _, (&str, nom::error::ErrorKind)>("]")(self.0) {
self.0 = i;
return Some(PacketContents::EndList);
} else if let Ok((i, x)) = u32::<_, (&str, nom::error::ErrorKind)>(self.0) {
self.0 = i;
return Some(PacketContents::Integer(x as usize));
} else if let Ok((i, _)) = tag::<_, _, (&str, nom::error::ErrorKind)>(",")(self.0) {
self.0 = i;
} else {
return None;
}
}
}
}
|
