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use std::collections::VecDeque;
static DAY: u8 = 15;
fn main() {
let input = advent::read_file(DAY);
println!("{DAY}a: {}", hash_sum(&input));
println!("{DAY}b: {}", focusing_power(&input));
}
fn hash(input: &str) -> usize {
let mut value = 0;
for c in input.chars() {
value += c as usize;
value *= 17;
value %= 256;
}
value
}
#[derive(Clone, Debug)]
struct Lens {
label: String,
focal_length: usize,
}
enum Operation {
Assign(Lens),
Remove(String),
}
impl Operation {
fn from(input: &str) -> Operation {
if let Some((label, value)) = input.split_once('=') {
Operation::Assign(Lens {
label: label.to_string(),
focal_length: value.parse().unwrap()
})
} else if let Some((label, _)) = input.split_once('-') {
Operation::Remove(label.to_string())
} else {
panic!("invalid operation");
}
}
fn label(&self) -> String {
match self {
Operation::Assign(lens) => lens.label.clone(),
Operation::Remove(label) => label.to_string(),
}
}
}
fn hash_sum(input: &str) -> usize {
let input = input.trim_end();
input.split(',')
.map(hash)
.sum()
}
fn init_sequence(boxes: &mut [VecDeque::<Lens>], operations: &[Operation]) {
for operation in operations {
let box_nr = hash(&operation.label());
match operation {
Operation::Assign(lens) => {
if let Some(boxed_lens) = boxes[box_nr].iter_mut().find(|l| l.label == lens.label) {
boxed_lens.focal_length = lens.focal_length;
} else {
boxes[box_nr].push_back(lens.clone());
}
},
Operation::Remove(label) => {
boxes[box_nr].retain(|lens| lens.label != *label);
}
}
}
}
fn focusing_power(input: &str) -> usize {
let input = input.trim_end();
let operations = input.split(',')
.map(Operation::from)
.collect::<Vec<_>>();
let mut boxes = vec![VecDeque::<Lens>::new(); 256];
init_sequence(&mut boxes, &operations);
boxes.iter()
.enumerate()
.map(|(box_nr, lenses)| lenses.iter().enumerate().map(|(slot, lens)| (box_nr + 1) * (slot + 1) * lens.focal_length).sum::<usize>())
.sum()
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test() {
let input = "rn=1,cm-,qp=3,cm=2,qp-,pc=4,ot=9,ab=5,pc-,pc=6,ot=7";
assert_eq!(hash("HASH"), 52);
assert_eq!(hash_sum(input), 1320);
assert_eq!(focusing_power(input), 145);
}
}
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