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use anyhow::Context as _;
use std::convert::TryInto as _;
use std::io::BufRead as _;
struct Line {
c: char,
n1: usize,
n2: usize,
password: String,
}
impl Line {
fn parse(line: &str) -> anyhow::Result<Self> {
let rx = regex::Regex::new(r"^([0-9]+)-([0-9]+) (.): (.*)$").unwrap();
let captures =
rx.captures(line).context("line failed to match regex")?;
let c = captures
.get(3)
.unwrap()
.as_str()
.parse()
.context("invalid policy char")?;
let n1 = captures
.get(1)
.unwrap()
.as_str()
.parse()
.context("invalid policy lower bound")?;
let n2 = captures
.get(2)
.unwrap()
.as_str()
.parse()
.context("invalid policy upper bound")?;
let password = captures.get(4).unwrap().as_str().to_string();
Ok(Self {
c,
n1,
n2,
password,
})
}
fn valid_part_1(&self) -> bool {
let count = self.password.chars().filter(|c| *c == self.c).count();
count >= self.n1 && count <= self.n2
}
fn valid_part_2(&self) -> bool {
(self.password.chars().nth(self.n1 - 1) == Some(self.c))
^ (self.password.chars().nth(self.n2 - 1) == Some(self.c))
}
}
pub fn part1() -> anyhow::Result<i64> {
let lines = read_lines()?;
let count = lines.iter().filter(|l| l.valid_part_1()).count();
Ok(count.try_into()?)
}
pub fn part2() -> anyhow::Result<i64> {
let lines = read_lines()?;
let count = lines.iter().filter(|l| l.valid_part_2()).count();
Ok(count.try_into()?)
}
fn read_lines() -> anyhow::Result<Vec<Line>> {
let f = std::fs::File::open("data/2.txt")
.context("couldn't find data file 2.txt")?;
let f = std::io::BufReader::new(f);
f.lines()
.map(|l| Line::parse(&l.context("failed to read a line")?))
.collect()
}
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