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|
use nom::{
branch::alt,
bytes::complete::tag,
character::complete::{line_ending, u32},
combinator::map,
multi::{separated_list0, separated_list1},
sequence::{delimited, pair, preceded},
IResult,
};
use std::{cmp::Ordering, fs};
fn main() -> Result<(), Box<dyn std::error::Error>> {
let input = fs::read_to_string("inputs/day_13.txt")?;
let message = EncodedMessage::parser(&input).unwrap().1;
dbg!(message.ordered_index_sum());
dbg!(message.decoder_key());
Ok(())
}
#[derive(Debug)]
struct EncodedMessage {
message_pairs: Vec<(Message, Message)>,
ordered_indices: Vec<usize>,
}
#[derive(Debug, Clone, PartialEq, Eq)]
enum Message {
List(Vec<Message>),
Value(u32),
}
impl EncodedMessage {
fn parser(input: &str) -> IResult<&str, Self> {
map(
separated_list1(
pair(line_ending, line_ending),
pair(Message::parser, preceded(line_ending, Message::parser)),
),
EncodedMessage::new,
)(input)
}
fn new(message_pairs: Vec<(Message, Message)>) -> EncodedMessage {
let mut ordered_indices = Vec::new();
for (i, (left, right)) in message_pairs.iter().enumerate() {
if left <= right {
ordered_indices.push(i + 1);
}
}
EncodedMessage {
message_pairs,
ordered_indices,
}
}
fn ordered_index_sum(&self) -> usize {
self.ordered_indices.iter().sum()
}
fn decoder_key(&self) -> usize {
let mut all_packets: Vec<Message> = self
.message_pairs
.iter()
.flat_map(|(left, right)| [left.clone(), right.clone()])
.collect();
let divider_1 = Message::List(vec![Message::List(vec![Message::Value(2)])]);
let divider_2 = Message::List(vec![Message::List(vec![Message::Value(6)])]);
all_packets.push(divider_1.clone());
all_packets.push(divider_2.clone());
all_packets.sort();
let index_1 = all_packets.iter().position(|m| *m == divider_1).unwrap() + 1;
let index_2 = all_packets.iter().position(|m| *m == divider_2).unwrap() + 1;
index_1 * index_2
}
}
impl Message {
fn parser(input: &str) -> IResult<&str, Self> {
alt((
map(u32, Message::Value),
map(
delimited(
tag("["),
separated_list0(tag(","), Message::parser),
tag("]"),
),
Message::List,
),
))(input)
}
}
impl PartialOrd for Message {
fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
Some(self.cmp(other))
}
}
impl Ord for Message {
fn cmp(&self, other: &Self) -> Ordering {
match (self, other) {
(Message::Value(left), Message::Value(right)) => left.cmp(right),
(Message::List(left), Message::List(right)) => {
for i in 0..left.len() {
if i == right.len() {
return Ordering::Greater;
}
let inner_ord = left[i].cmp(&right[i]);
if inner_ord != Ordering::Equal {
return inner_ord;
}
}
left.len().cmp(&right.len())
}
(Message::Value(left), Message::List(right)) => {
if right.len() == 0 {
Ordering::Greater
} else {
let inner_ord = Message::Value(*left).cmp(&right[0]);
if inner_ord != Ordering::Equal {
inner_ord
} else {
1.cmp(&right.len())
}
}
}
(Message::List(left), Message::Value(right)) => {
if left.len() == 0 {
Ordering::Less
} else {
let inner_ord = left[0].cmp(&Message::Value(*right));
if inner_ord != Ordering::Equal {
inner_ord
} else {
left.len().cmp(&1)
}
}
}
}
}
}
|
