65 lines
1.5 KiB
Rust
65 lines
1.5 KiB
Rust
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use std::fmt::Write;
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use aoc::err;
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const INPUT: &str = include_str!("../input/day13.txt");
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pub fn run() -> aoc::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 part1(input: &str) -> aoc::Result<u64> {
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let mut lines = input.lines();
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let earliest_timestamp = lines
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.next()
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.ok_or_else(|| err!("input was empty"))?
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.parse::<u64>()
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.map_err(|e| err!("couldn't parse first line: {}", e))?;
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let bus_ids = lines
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.next()
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.ok_or_else(|| err!("no second line"))?
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.split(',')
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.filter_map(|num| {
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if num == "x" {
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None
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} else {
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Some(num.parse::<u64>().map_err(|e| err!("{}", e)))
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}
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})
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.collect::<aoc::Result<Vec<_>>>()?;
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let (bus_id, earliest_departure) = bus_ids
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.iter()
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.map(|id| {
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let next_departure = ((earliest_timestamp / id) * id) + id;
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(id, next_departure)
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})
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.min_by_key(|(_, next_departure)| *next_departure)
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.unwrap();
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Ok(bus_id * (earliest_departure - earliest_timestamp))
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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/day13_provided.txt");
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#[test]
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fn part1_provided() {
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assert_eq!(part1(PROVIDED).unwrap(), 295);
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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(), 3269);
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}
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}
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