89 lines
2.2 KiB
Rust
89 lines
2.2 KiB
Rust
//! Day 07 of 2020.
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use crate::prelude::*;
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/// Get the solution for day 07 of 2020.
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pub fn solution() -> Solution {
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Solution::new(Day::new(7, 2020), part_1, part_2).with_expected(169, 82372)
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}
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/// The target bag to look for.
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const TARGET: &str = "shiny gold";
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/// Parse the bags from the puzzle input.
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fn parse_bags(input: &str) -> Vec<(&str, Vec<(usize, &str)>)> {
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let mut bags = vec![];
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for line in input.lines() {
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let main_bag = &line[0..line.find(" bags").unwrap()];
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let other_bags = line[line.find("contain ").unwrap() + "contain ".len()..]
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.split(',')
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.map(str::trim)
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.map(|bag| {
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let count = bag[0..bag.find(' ').unwrap()]
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.parse::<usize>()
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.unwrap_or_default();
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let bag = &bag[bag.find(' ').unwrap() + 1..bag.find(" bag").unwrap()];
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(count, bag)
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})
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.collect::<Vec<(usize, &str)>>();
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bags.push((main_bag, other_bags));
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}
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bags
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}
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/// Find out which bags can hold the [`TARGET`] bag.
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fn can_hold_target_bag<'a>(
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target: &'a str,
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bags: &[(&'a str, Vec<(usize, &'a str)>)],
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) -> Vec<&'a str> {
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let mut can_hold = vec![];
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for (bag, children) in bags {
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if children.iter().any(|(_, child)| *child == target) {
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can_hold.push(*bag);
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can_hold.append(&mut can_hold_target_bag(bag, bags));
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}
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}
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can_hold
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}
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/// Find out how many bags are required to be inside the [`TARGET`] bag.
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fn target_bag_holds_amount<'a>(
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target: &'a str,
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bags: &[(&'a str, Vec<(usize, &'a str)>)],
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) -> usize {
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let mut count = 0;
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for (bag, children) in bags {
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if bag == &target {
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for (child_count, child_bag) in children {
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if child_count != &0 {
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count += child_count;
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count += child_count * target_bag_holds_amount(child_bag, bags);
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}
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}
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}
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}
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count
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}
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/// The logic to solve part one.
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fn part_1(input: &str) -> Result<String> {
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Ok(
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can_hold_target_bag(TARGET, &parse_bags(input))
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.into_iter()
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.collect::<HashSet<&str>>()
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.len()
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.to_string(),
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)
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}
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/// The logic to solve part two.
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fn part_2(input: &str) -> Result<String> {
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Ok(target_bag_holds_amount("shiny gold", &parse_bags(input)).to_string())
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}
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