johannes/advent-of-rust-2024
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day 16 part 2 speedup x2

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Johannes
2024-12-16 21:25:30 +01:00
parent fbc80cac85
commit 1469d51ba7
1 changed files with 45 additions and 15 deletions
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60
src/day16.rs
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@@ -1,5 +1,5 @@
use std::{
collections::{BinaryHeap, HashMap},
collections::{BinaryHeap, HashMap, HashSet},
fs::read_to_string,
};
@@ -33,7 +33,7 @@ impl Dir {
}
}
struct Step(Coord, Dir, usize, Vec<Coord>);
struct Step(Coord, Dir, usize, Option<Node>);
impl Ord for Step {
fn cmp(&self, other: &Self) -> std::cmp::Ordering {
@@ -59,7 +59,7 @@ fn part1(input: &str) -> RiddleResult {
let end = maze.entries().find(|(_p, c)| **c == 'E').unwrap().0;
let mut visited = HashMap::<(Coord, Dir), usize>::new();
let mut stack: BinaryHeap<Step> = BinaryHeap::new();
stack.push(Step(start, E, 0, vec![]));
stack.push(Step(start, E, 0, None));
while let Some(Step(np, nd, cost, _)) = stack.pop() {
if visited.contains_key(&(np, nd)) {
continue;
@@ -70,7 +70,7 @@ fn part1(input: &str) -> RiddleResult {
}
for d in nd.nexts() {
if !visited.contains_key(&(np, d)) {
stack.push(Step(np, d, cost + 1000, vec![]));
stack.push(Step(np, d, cost + 1000, None));
}
}
let forward = match nd {
@@ -80,38 +80,52 @@ fn part1(input: &str) -> RiddleResult {
W => (np.0 - 1, np.1),
};
if maze[forward] != '#' && !visited.contains_key(&(forward, nd)) {
stack.push(Step(forward, nd, cost + 1, vec![]));
stack.push(Step(forward, nd, cost + 1, None));
}
}
panic!("no path found")
}
type Node = (Coord, Dir);
fn part2(input: &str) -> RiddleResult {
use Dir::*;
let maze = Grid::parse(input);
let start = maze.entries().find(|(_p, c)| **c == 'S').unwrap().0;
let end = maze.entries().find(|(_p, c)| **c == 'E').unwrap().0;
let mut visited = HashMap::<(Coord, Dir), usize>::new();
let mut visited = HashMap::<Node, (usize, Vec<Node>)>::new();
let mut stack: BinaryHeap<Step> = BinaryHeap::new();
stack.push(Step(start, E, 0, vec![]));
stack.push(Step(start, E, 0, None));
let mut best: Option<usize> = None;
let mut visited_by_best: Vec<Coord> = vec![start, end];
while let Some(Step(np, nd, cost, mut pred)) = stack.pop() {
while let Some(Step(np, nd, cost, pred)) = stack.pop() {
if let Some(b) = best {
if b < cost {
break; // can't reach the end point with best cost anymore
}
}
visited.insert((np, nd), cost);
let entry = visited.entry((np, nd)).or_insert_with(|| {
(
cost,
if let Some(pred) = pred {
vec![pred]
} else {
vec![]
},
)
});
if entry.0 < cost {
continue;
}
if let Some(pred) = pred {
entry.1.push(pred);
}
if np == end {
best = Some(cost);
visited_by_best.append(&mut pred);
}
pred.push(np);
for d in nd.nexts() {
if !visited.contains_key(&(np, d)) {
stack.push(Step(np, d, cost + 1000, pred.clone()));
stack.push(Step(np, d, cost + 1000, Some((np, nd))));
}
}
let forward = match nd {
@@ -121,10 +135,26 @@ fn part2(input: &str) -> RiddleResult {
W => (np.0 - 1, np.1),
};
if maze[forward] != '#' && !visited.contains_key(&(forward, nd)) {
stack.push(Step(forward, nd, cost + 1, pred));
stack.push(Step(forward, nd, cost + 1, Some((np, nd))));
}
}
visited_by_best.into_iter().unique().count()
let mut accounted = HashSet::<Node>::new();
let mut stack: Vec<Node> = visited
.iter()
.filter(|((pos, _dir), _)| *pos == end)
.map(|(node, _)| *node)
.to_owned()
.collect_vec();
while let Some(node) = stack.pop() {
if accounted.contains(&node) {
continue;
}
accounted.insert(node);
for pred in visited[&node].1.iter() {
stack.push(*pred);
}
}
accounted.into_iter().map(|(pos, _)| pos).unique().count()
}
#[cfg(test)]