96 lines
2.2 KiB
Rust
96 lines
2.2 KiB
Rust
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use std::cmp::Ordering;
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use std::collections::VecDeque;
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use std::fmt::Write;
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use anyhow::{Context, Result};
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const INPUT: &str = include_str!("../input/day22.txt");
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pub fn run() -> Result<String> {
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let mut res = String::with_capacity(128);
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writeln!(res, "part 1: {}", part1(INPUT)?)?;
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Ok(res)
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}
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fn play_game<'a>(deck_a: &'a mut Deck, deck_b: &'a mut Deck) -> &'a Deck {
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while !(deck_a.0.is_empty() || deck_b.0.is_empty()) {
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let card_a = deck_a.0.pop_front().unwrap();
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let card_b = deck_b.0.pop_front().unwrap();
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match card_a.cmp(&card_b) {
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Ordering::Greater => {
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deck_a.0.push_back(card_a);
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deck_a.0.push_back(card_b);
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}
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Ordering::Less => {
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deck_b.0.push_back(card_b);
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deck_b.0.push_back(card_a);
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}
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Ordering::Equal => unreachable!(),
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}
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}
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if deck_a.0.is_empty() {
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deck_b
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} else {
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deck_a
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}
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}
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fn part1(input: &str) -> Result<u64> {
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let mut decks = input.split("\n\n");
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let mut deck_a: Deck = decks.next().context("couldn't get first deck")?.parse()?;
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let mut deck_b: Deck = decks.next().context("couldn't get second deck")?.parse()?;
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let winning_deck = play_game(&mut deck_a, &mut deck_b);
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Ok(winning_deck
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.0
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.iter()
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.rev()
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.enumerate()
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.map(|(i, card)| card * (i as u64 + 1))
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.sum())
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}
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struct Deck(VecDeque<u64>);
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impl Deck {}
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impl std::str::FromStr for Deck {
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type Err = anyhow::Error;
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fn from_str(s: &str) -> Result<Self> {
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let mut lines = s.lines();
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// `Player N:`
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lines.next().context("couldn't skip first line")?;
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let deck = lines
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.map(|line| line.parse().map_err(anyhow::Error::new))
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.collect::<Result<_>>()?;
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Ok(Self(deck))
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}
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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const PROVIDED: &str = include_str!("../input/day22_provided.txt");
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#[test]
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fn part1_provided() {
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assert_eq!(part1(PROVIDED).unwrap(), 306);
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}
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#[test]
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fn part1_real() {
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assert_eq!(part1(INPUT).unwrap(), 30780);
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}
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}
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