110 lines
2.5 KiB
Rust
110 lines
2.5 KiB
Rust
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use std::fmt::Write;
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use std::ops::RangeInclusive;
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use std::str::FromStr;
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use aoc::{err, Result};
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const INPUT: &str = include_str!("../input/day02.txt");
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#[derive(Debug)]
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struct PassPolicy {
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repetitions: RangeInclusive<usize>,
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letter: u8,
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password: String,
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}
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impl PassPolicy {
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fn new(repetitions: RangeInclusive<usize>, letter: u8, password: String) -> Self {
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Self {
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repetitions,
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letter,
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password,
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}
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}
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#[allow(clippy::naive_bytecount)] // let's not pull a crate just for that
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fn is_valid(&self) -> bool {
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let occurrences = self
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.password
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.as_bytes()
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.iter()
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.filter(|&&b| b == self.letter)
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.count();
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self.repetitions.contains(&occurrences)
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}
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}
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impl FromStr for PassPolicy {
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type Err = aoc::Error;
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fn from_str(s: &str) -> Result<Self> {
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let s = s.trim_end();
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let space = s
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.find(' ')
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.ok_or_else(|| err!("couldn't parse password policy: didn't find space"))?;
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let dash = s
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.find('-')
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.ok_or_else(|| err!("couldn't parse password policy: didn't find dash"))?;
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let min_bound = s[..dash]
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.parse::<usize>()
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.map_err(|e| err!("couldn't parse range: {}", e))?;
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let max_bound = s[(dash + 1)..space]
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.parse::<usize>()
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.map_err(|e| err!("couldn't parse range: {}", e))?;
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let colon = s
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.find(':')
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.ok_or_else(|| err!("couldn't parse password policy: didn't find colon"))?;
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let letter = s.as_bytes()[colon - 1];
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let password = &s[(colon + 2)..];
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Ok(Self::new(
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min_bound..=max_bound,
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letter,
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password.to_string(),
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))
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}
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}
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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 part1(input: &str) -> Result<usize> {
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let policies = input
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.lines()
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.map(|line| line.parse::<PassPolicy>().map_err(|e| err!("{}", e)))
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.collect::<Result<Vec<PassPolicy>>>()?;
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Ok(policies.iter().filter(|policy| policy.is_valid()).count())
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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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static PROVIDED: &'static str = "1-3 a: abcde
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1-3 b: cdefg
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2-9 c: ccccccccc
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";
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#[test]
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fn part1_provided() {
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assert_eq!(part1(PROVIDED).unwrap(), 2);
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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(), 556);
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}
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}
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