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Reduce runtime by 90% by eliminating hashsets

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Bert Peters
2023-12-25 00:58:40 +01:00
parent 898f8dce25
commit 0af116920b
1 changed files with 13 additions and 11 deletions
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24
2023/src/day23.rs
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@@ -1,5 +1,4 @@
use std::collections::HashMap;
use std::collections::HashSet;
use crate::common::Grid;
use crate::common::IndexSet;
@@ -121,7 +120,7 @@ fn longest_path(
pos: usize,
travelled: u32,
graph: &[Vec<(Slope, usize, u32)>],
visited: &mut HashSet<usize>,
visited: u64,
) -> u32 {
if pos == 1 {
return travelled;
@@ -130,9 +129,12 @@ fn longest_path(
let mut best = 0;
for &(slope, other, dist) in &graph[pos] {
if !matches!(slope, Slope::Up) && visited.insert(other) {
best = Ord::max(best, longest_path(other, travelled + dist, graph, visited));
visited.remove(&other);
let index = 1u64 << other;
if !matches!(slope, Slope::Up) && (visited & index) == 0 {
best = Ord::max(
best,
longest_path(other, travelled + dist, graph, visited | index),
);
}
}
@@ -142,14 +144,14 @@ fn longest_path(
pub fn part1(input: &[u8]) -> anyhow::Result<String> {
let graph = simplify_graph(input)?;
Ok(longest_path(0, 0, &graph, &mut HashSet::new()).to_string())
Ok(longest_path(0, 0, &graph, 0).to_string())
}
fn longer_longest_path(
pos: usize,
travelled: u32,
graph: &[Vec<(Slope, usize, u32)>],
visited: &mut HashSet<usize>,
visited: u64,
) -> u32 {
if pos == 1 {
return travelled;
@@ -158,12 +160,12 @@ fn longer_longest_path(
let mut best = 0;
for &(_, other, dist) in &graph[pos] {
if visited.insert(other) {
let index = 1u64 << other;
if (visited & index) == 0 {
best = Ord::max(
best,
longer_longest_path(other, travelled + dist, graph, visited),
longer_longest_path(other, travelled + dist, graph, visited | index),
);
visited.remove(&other);
}
}
@@ -173,7 +175,7 @@ fn longer_longest_path(
pub fn part2(input: &[u8]) -> anyhow::Result<String> {
let graph = simplify_graph(input)?;
Ok(longer_longest_path(0, 0, &graph, &mut HashSet::new()).to_string())
Ok(longer_longest_path(0, 0, &graph, 0).to_string())
}
#[cfg(test)]