jonas.tngl.sh
Advent of Code solutions in Rust
feat: part 1 of day 13 of AoC 2020
+93
-2
+91
aoc_2020/src/day13.rs
+91
aoc_2020/src/day13.rs
···
1
+
use anyhow::{Context, anyhow, bail};
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use aoc_companion::prelude::*;
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use itertools::Itertools as _;
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use std::str::FromStr;
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pub(crate) struct Door {
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arrival_time: u64,
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bus_schedule: Vec<BusLine>,
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}
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impl<'input> Solution<'input> for Door {
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fn parse(input: &'input str) -> Result<Self> {
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let Some((arrival_line, buses_line)) = input.split_once('\n') else {
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bail!(
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"expected exactly two lines, got {} lines",
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input.lines().count()
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)
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};
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Ok(Self {
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arrival_time: arrival_line.parse().context("invalid arrival time")?,
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bus_schedule: buses_line.split(',').map(str::parse).try_collect()?,
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})
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}
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fn part1(&self) -> Result<u64> {
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earliest_departure(self.arrival_time, &self.bus_schedule)
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.ok_or_else(|| anyhow!("no buses scheduled"))
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}
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}
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enum BusLine {
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BusId(u64),
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Omission,
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}
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impl FromStr for BusLine {
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type Err = anyhow::Error;
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fn from_str(s: &str) -> Result<Self> {
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Ok(match s {
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"x" => BusLine::Omission,
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_ => BusLine::BusId(
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s.parse()
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.context("bus line must be either 'x' or a positive number")?,
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),
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})
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}
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}
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impl BusLine {
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fn id(&self) -> Option<u64> {
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match self {
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BusLine::BusId(id) => Some(*id),
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BusLine::Omission => None,
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}
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}
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}
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fn earliest_departure(arrival: u64, schedule: &[BusLine]) -> Option<u64> {
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schedule
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.iter()
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.filter_map(|bus| bus.id())
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.min_by_key(|id| id - arrival % id)
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.map(|min_id| min_id * (min_id - arrival % min_id))
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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 EXAMPLE_ARRIVAL: u64 = 939;
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const EXAMPLE_SCHEDULE: [BusLine; 8] = [
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BusLine::BusId(7),
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BusLine::BusId(13),
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BusLine::Omission,
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BusLine::Omission,
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BusLine::BusId(59),
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BusLine::Omission,
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BusLine::BusId(31),
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BusLine::BusId(19),
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];
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#[test]
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fn find_earliest_bus_in_example() {
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assert_eq!(
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earliest_departure(EXAMPLE_ARRIVAL, &EXAMPLE_SCHEDULE),
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Some(295)
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);
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}
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}
+2
-2
aoc_2020/src/main.rs
+2
-2
aoc_2020/src/main.rs
···
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12
mod day10;
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mod day11;
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mod day12;
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-
// mod day13;
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mod day13;
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// mod day14;
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// mod day15;
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// mod day16;
···
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door!(2020-12-10 ~> day10),
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door!(2020-12-11 ~> day11),
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door!(2020-12-12 ~> day12),
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// door!(2020-12-13 ~> day13),
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door!(2020-12-13 ~> day13),
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// door!(2020-12-14 ~> day14),
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// door!(2020-12-15 ~> day15),
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// door!(2020-12-16 ~> day16),