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use std::{cmp::Ordering, fmt, str::FromStr};
#[derive(PartialEq, Eq, Clone)]
enum ListItem {
List(Vec<ListItem>),
Number(usize),
}
impl fmt::Debug for ListItem {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match self {
ListItem::List(arr) => f.debug_list().entries(arr.iter()).finish(),
ListItem::Number(num) => write!(f, "{}", num),
}
}
}
impl ListItem {
fn with_slice<T>(&self, f: impl FnOnce(&[ListItem]) -> T) -> T {
match self {
Self::List(n) => f(&n[..]),
Self::Number(n) => f(&[Self::Number(*n)]),
}
}
}
impl std::cmp::Ord for ListItem {
fn cmp(&self, other: &Self) -> Ordering {
self.partial_cmp(other).unwrap()
}
}
impl PartialOrd for ListItem {
fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
match (self, other) {
(ListItem::Number(a), ListItem::Number(b)) => a.partial_cmp(b),
(l, r) => l.with_slice(|l| r.with_slice(|r| l.partial_cmp(r))),
}
}
}
impl FromStr for ListItem {
type Err = String;
fn from_str(input: &str) -> Result<Self, Self::Err> {
// Remove whitespace from input
let input = input.trim();
// Check if input is empty
if input.is_empty() {
return Ok(ListItem::List(vec![]));
}
// Check if input is a number
if let Ok(num) = input.parse::<usize>() {
return Ok(ListItem::Number(num));
}
// Check if input is a list
if input.starts_with('[') && input.ends_with(']') {
// Remove brackets from input
let input = &input[1..input.len() - 1];
// Split input by commas
let mut items = Vec::new();
let mut start = 0;
let mut level = 0;
for (i, c) in input.char_indices() {
match c {
'[' => level += 1,
']' => level -= 1,
',' if level == 0 => {
// Parse a list item
let item = ListItem::from_str(&input[start..i])?;
items.push(item);
start = i + 1;
}
_ => {}
}
}
// Parse the last list item
let item = ListItem::from_str(&input[start..])?;
items.push(item);
return Ok(ListItem::List(items));
}
// Invalid input
Err("Invalid input".to_string())
}
}
type Packet = ListItem;
#[derive(Debug)]
struct PacketPair {
left: Packet,
right: Packet,
}
// [[1],[2,3,4]]
fn solve_part_one(data: &str) -> usize {
let packets_pairs: Vec<&str> = data.split("\n\n").collect();
let mut packets: Vec<PacketPair> = vec![];
for pair in packets_pairs {
let (first, last) = pair
.split_once("\n")
.expect("Should be splittable by newline");
let first = ListItem::from_str(first).unwrap();
let last = ListItem::from_str(last).unwrap();
packets.push(PacketPair {
left: first,
right: last,
});
}
let mut ans = 0;
for (i, pair) in packets.iter().enumerate() {
if pair.left < pair.right {
ans += i + 1;
}
}
ans
}
fn solve_part_two(data: &str) -> usize {
let dividers = vec![
Packet::List(vec![Packet::Number(2)]),
Packet::List(vec![Packet::Number(6)]),
];
let mut packets = data
.lines()
.filter(|s| !s.is_empty())
.map(|line| Packet::from_str(line).unwrap())
.chain(dividers.iter().cloned())
.collect::<Vec<_>>();
packets.sort();
dividers
.iter()
.map(|d| packets.binary_search(d).unwrap() + 1)
.product::<usize>()
}
fn main() {
let test = include_str!("../input/day13.test");
let prod = include_str!("../input/day13.prod");
println!("Part1_test : {}", solve_part_one(test));
println!("Part1_prod : {}", solve_part_one(prod));
println!("{}", solve_part_two(test));
println!("{}", solve_part_two(prod));
}
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