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mod utils;
use std::collections::HashSet;
use utils::read_input;
fn main() {
let input = read_input();
// Convert each line to a tuple of hashsets, one for each backpack pocket
let rucksack_items: Vec<_> = input
.lines()
.map(|line| (&line[..line.len() / 2], &line[line.len() / 2..]))
.map(|(a, b)| -> (HashSet<char>, HashSet<char>) {
(a.chars().collect(), b.chars().collect())
})
.collect();
let sum_error_priorities: u32 = rucksack_items
.iter()
.map(|(a, b)| {
*a.intersection(b)
.next()
.expect("no common item between two backpack segments!")
}) // Get common item
.map(priority)
.sum();
let sum_badge_priorities: u32 = rucksack_items // Construct chunked iterator
.iter()
.step_by(3)
.zip(rucksack_items.iter().skip(1).step_by(3))
.zip(rucksack_items.iter().skip(2).step_by(3))
.map(|(((e1l, e1r), (e2l, e2r)), (e3l, e3r))| {
for item in e1l.union(e1r) {
if (e2l.contains(item) || e2r.contains(item))
&& (e3l.contains(item) || e3r.contains(item))
{
return *item;
}
}
panic!(
"group has no badge! {:?}",
((e1l, e1r), (e2l, e2r), (e3l, e3r))
)
})
.map(priority)
.sum();
println!("Part 1: {}", sum_error_priorities);
println!("Part 2: {}", sum_badge_priorities);
}
fn priority(chr: char) -> u32 {
if chr.is_ascii_lowercase() {
chr as u32 - 96
} else if chr.is_ascii_uppercase() {
chr as u32 - 38
} else {
panic!("unrecognised item {}", chr)
}
}
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