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some cleanup

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This commit is contained in:
Glenn Griffin 2020-12-10 11:03:09 -08:00
parent 99ed36f50a
commit 0d372dfdb1
1 changed files with 15 additions and 9 deletions
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22
src/day10.rs
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@ -1,6 +1,6 @@
use aoc_runner_derive::aoc;
#[derive(Debug,Copy,Clone,PartialEq,Eq,PartialOrd,Ord)]
#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord)]
struct Jolts(usize);
impl std::ops::Add for Jolts {
type Output = Jolts;
@ -56,17 +56,23 @@ pub fn solve_d10_p2(input: &str) -> usize {
// To calculate the number of combinations the current adapter has you first
// determine which are the potential upstream adapters and then sum their
// combinations.
let mut combinations_count = Vec::with_capacity(jolts.len());
combinations_count.push(1);
for (idx, current_jolts) in jolts.iter().copied().enumerate().skip(1) {
let mut adapter_paths_to_zero = 0;
for upstream_idx in idx.saturating_sub(3) .. idx {
let mut combinations_count = Vec::with_capacity(jolts.len());
// The first entry in jolts is the `0` jolts. Initialize it with 1 to
// indicate that it is the only way to reach the end of the chain.
combinations_count.push(1);
// Skip the first entry in jolts since it's already initialized in
// combinations_count.
for (idx, current_jolts) in jolts.iter().copied().enumerate().skip(1) {
let mut current_combinations = 0;
for upstream_idx in idx.saturating_sub(3)..idx {
if current_jolts - jolts[upstream_idx] <= Jolts(3) {
adapter_paths_to_zero += combinations_count[upstream_idx];
current_combinations += combinations_count[upstream_idx];
}
}
combinations_count.push(adapter_paths_to_zero);
combinations_count.push(current_combinations);
}
*combinations_count.last().unwrap()
}