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use std::collections::HashMap;
use anyhow::Context;
use crate::{Problem, Solution};
pub struct Day15;
impl Problem for Day15 {
const DAY: u8 = 15;
const INPUT: &'static str = include_str!("../input/day_15.txt");
}
impl Solution for Day15 {
type Answer1 = usize;
type Answer2 = usize;
fn part_1(input: &str) -> anyhow::Result<Self::Answer1> {
Ok(input.trim().split(',').map(hash).sum())
// 509784 ==
}
fn part_2(input: &str) -> anyhow::Result<Self::Answer2> {
Ok(input
.trim()
.split(',')
.try_fold(Boxes::new(), process_step)?
.into_iter()
.map(calculate_power)
.sum())
// 339464 >
// 230197 ==
}
}
type Lenses = Vec<(String, usize)>;
type Boxes = HashMap<usize, Lenses>;
fn hash(s: &str) -> usize {
s.trim()
.chars()
.fold(0, |acc, c| (acc + c as usize) * 17 % 256)
}
fn process_step(mut acc: Boxes, s: &str) -> anyhow::Result<Boxes> {
let (label, power) = s.split_once(['-', '=']).context("Failed to parse input")?;
let key = hash(label);
let lenses = acc.entry(key).or_default();
match lenses.iter().position(|(s, _)| s == label) {
pos if !power.is_empty() => {
lenses.push((label.to_owned(), power.parse()?));
if let Some(index) = pos {
lenses.swap_remove(index);
}
}
Some(index) => {
lenses.remove(index);
if lenses.is_empty() {
acc.remove(&key);
}
}
_ => {}
};
Ok(acc)
}
fn calculate_power((id, lenses): (usize, Lenses)) -> usize {
lenses
.into_iter()
.enumerate()
.map(|(i, (_, len))| (id + 1) * (i + 1) * len)
.sum::<usize>()
}
#[cfg(test)]
mod tests {
use super::*;
const INPUT: &str = "rn=1,cm-,qp=3,cm=2,qp-,pc=4,ot=9,ab=5,pc-,pc=6,ot=7";
#[test]
fn test_part_1() -> anyhow::Result<()> {
Ok(assert_eq!(1320, Day15::part_1(INPUT)?))
}
#[test]
fn test_part_2() -> anyhow::Result<()> {
Ok(assert_eq!(145, Day15::part_2(INPUT)?))
}
}
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