79 lines
2.7 KiB
Rust
79 lines
2.7 KiB
Rust
use aoc_runner_derive::aoc;
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#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord)]
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struct Jolts(usize);
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impl std::ops::Add for Jolts {
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type Output = Jolts;
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fn add(self, b: Jolts) -> Jolts {
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Jolts(self.0 + b.0)
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}
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}
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impl std::ops::Sub for Jolts {
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type Output = Jolts;
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fn sub(self, b: Jolts) -> Jolts {
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Jolts(self.0 - b.0)
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}
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}
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#[aoc(day10, part1)]
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pub fn solve_d10_p1(input: &str) -> usize {
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let jolts = {
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let mut jolts: Vec<Jolts> = std::iter::once(Jolts(0))
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.chain(input.split('\n').map(|x| Jolts(x.parse().unwrap())))
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.collect();
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jolts.sort();
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jolts.push(*jolts.last().unwrap() + Jolts(3)); // The devices built-in adapter is always 3 more than the highest.
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jolts
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};
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// Count the number of 1-jolt differences and 3-jolt differences in the
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// chain.
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let (j1_diff, j3_diff) =
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jolts
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.windows(2)
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.fold((0, 0), |(j1_diff, j3_diff), entry| match entry {
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&[a, b] if b - a == Jolts(1) => (j1_diff + 1, j3_diff),
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&[a, b] if b - a == Jolts(3) => (j1_diff, j3_diff + 1),
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_ => panic!("fail"),
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});
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j1_diff * j3_diff
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}
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#[aoc(day10, part2)]
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pub fn solve_d10_p2(input: &str) -> usize {
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let jolts = {
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let mut jolts: Vec<Jolts> = std::iter::once(Jolts(0))
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.chain(input.split('\n').map(|x| Jolts(x.parse().unwrap())))
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.collect();
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jolts.sort();
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jolts.push(*jolts.last().unwrap() + Jolts(3)); // The devices built-in adapter is always 3 more than the highest.
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jolts
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};
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// Iterate over the list of jolt value for the adapters. For each entry
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// store the number of combinations this adapter has that lead back to zero
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// in `combinations_count`
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// To calculate the number of combinations the current adapter has you first
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// determine which are the potential upstream adapters and then sum their
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// combinations.
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let mut combinations_count = Vec::with_capacity(jolts.len());
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// The first entry in jolts is the `0` jolts. Initialize it with 1 to
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// indicate that it is the only way to reach the end of the chain.
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combinations_count.push(1);
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// Skip the first entry in jolts since it's already initialized in
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// combinations_count.
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for (idx, current_jolts) in jolts.iter().copied().enumerate().skip(1) {
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let mut current_combinations = 0;
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for upstream_idx in idx.saturating_sub(3)..idx {
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if current_jolts - jolts[upstream_idx] <= Jolts(3) {
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current_combinations += combinations_count[upstream_idx];
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}
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}
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combinations_count.push(current_combinations);
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}
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*combinations_count.last().unwrap()
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}
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