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use {
anyhow::{
anyhow,
Context,
Result,
},
std::{
env::args,
fs::File,
io::{
BufRead,
BufReader,
},
path::Path,
},
};
fn item_priority(item: char) -> Option<usize> {
match item {
'a'..='z' => Some((item as u32 - 'a' as u32 + 1) as usize),
'A'..='Z' => Some((item as u32 - 'A' as u32 + 27) as usize),
_ => None,
}
}
#[derive(Debug)]
struct Rucksack {
compartments: Vec<String>,
}
impl Rucksack {
fn new(items: &str) -> Self {
let (first, second) = items.split_at(items.len()/2);
let compartments = vec![String::from(first), String::from(second)];
Self {
compartments,
}
}
fn contains(&self, needle: char) -> bool {
self.compartments[0].contains(needle) || self.compartments[1].contains(needle)
}
fn common_items(&self) -> String {
self.compartments[0].chars().filter(|item| self.compartments[1].contains(*item)).collect()
}
fn find_badge(&self, other: &Rucksack) -> String {
self.compartments[0].chars().chain(self.compartments[1].chars()).filter(|item|
other.contains(*item)).collect()
}
}
fn read_input<T: AsRef<Path>>(filename: T) -> Result<Vec<Rucksack>> {
let reader = BufReader::new(File::open(filename)?);
reader.lines().map(
|v| {
let s = v?;
Ok(Rucksack::new(&s))
}
).collect()
}
fn part1(input: &[Rucksack]) -> Result<usize> {
Ok(input.iter().filter_map(|rucksack| {
if let Some(item) = rucksack.common_items().chars().next() {
item_priority(item)
} else {
None
}
}).sum())
}
fn part2(input: &[Rucksack]) -> Result<usize> {
Ok(input.chunks(3).filter_map(|rucksacks| {
let some_candidates = rucksacks[0].find_badge(&rucksacks[1]);
let other_candidates = rucksacks[0].find_badge(&rucksacks[2]);
let common: String = some_candidates.chars().filter(|item|
other_candidates.contains(*item)).collect();
if let Some(item) = common.chars().next() {
item_priority(item)
} else {
None
}
}).sum())
}
fn main() -> Result<()> {
let ( do_part_1, do_part_2 ) = aoc::do_parts();
let filename = args().nth(1).ok_or_else(|| anyhow!("Missing input filename"))?;
let input = read_input(filename).context("Could not read input")?;
if do_part_1 {
let solution = part1(&input).context("No solution for part 1")?;
println!("Part1, solution found to be: {}", solution);
}
if do_part_2 {
let solution = part2(&input).context("No solution for part 2")?;
println!("Part2, solution found to be: {}", solution);
}
Ok(())
}
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