Stolen dijkstra time
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This commit is contained in:
Julius 2021-12-15 19:39:26 +01:00
parent 073a0dbcdc
commit a3961cbff0
Signed by: j00lz
GPG key ID: AF241B0AA237BBA2

View file

@ -1,9 +1,11 @@
use std::cmp::max;
use std::collections::{HashMap, HashSet};
use std::cmp::{max, Reverse};
use std::collections::{BinaryHeap, BTreeMap, HashMap};
use crate::Day;
type Coordinate = (usize, usize);
type Graph<V, E> = BTreeMap<V, BTreeMap<V, E>>;
pub struct Day15(HashMap<Coordinate, u32>, usize, usize);
impl Day for Day15 {
@ -23,8 +25,10 @@ impl Day for Day15 {
}
fn part1(&self) -> anyhow::Result<String> {
let r = do_part_1(&self.0, (self.1, self.1));
Ok(format!("{}", r))
let g = map_to_graph(&self.0, (self.1, self.1));
let end = &(self.1, self.2);
let r = dijkstra(&g, &(0, 0), end).unwrap();
Ok(format!("{}", r.1))
}
fn part2(&self) -> anyhow::Result<String> {
@ -37,7 +41,6 @@ impl Day for Day15 {
for ry in 0..5 {
for rx in 0..5 {
let coord = (rx * len + x, ry * len + y);
// println!("{:?}", coord);
let e = m.entry(coord).or_insert(0);
*e = orig_value + rx as u32 + ry as u32;
if *e > 9 {
@ -47,7 +50,11 @@ impl Day for Day15 {
}
}
}
Ok(format!("{}", do_part_1(&m, (len * 5 - 1, len * 5 - 1))))
let target = (len * 5 - 1, len * 5 - 1);
let g = map_to_graph(&m, target);
let r = dijkstra(&g, &(0, 0), &target).unwrap();
Ok(format!("{}", r.1))
}
}
@ -60,33 +67,63 @@ fn neighbours((x, y): Coordinate, (tx, ty): Coordinate) -> impl Iterator<Item=Co
].into_iter().flatten()
}
pub fn dijkstra(
graph: &Graph<Coordinate, u32>,
start: &Coordinate,
end: &Coordinate,
) -> Option<(Coordinate, u32)> {
let mut ans = BTreeMap::new();
let mut prio = BinaryHeap::new();
fn do_part_1(map: &HashMap<Coordinate, u32>, target: Coordinate) -> u32 {
let mut distance = HashMap::new();
let mut seen = HashSet::new();
let mut heap = vec![(0, 0)];
distance.insert((0, 0), 0);
// start is the special case that doesn't have a predecessor
ans.insert(*start, None);
while !heap.is_empty() {
heap.sort_unstable_by(|a, b| distance.get(b).unwrap().cmp(distance.get(a).unwrap()));
for (new, weight) in &graph[start] {
ans.insert(*new, Some((*start, *weight)));
prio.push(Reverse((*weight, new, start)));
}
let nearest = heap.pop().unwrap();
if nearest == target {
break;
while let Some(Reverse((dist_new, new, prev))) = prio.pop() {
match ans[new] {
// what we popped is what is in ans, we'll compute it
Some((p, d)) if p == *prev && d == dist_new => {}
// otherwise it's not interesting
_ => continue,
}
seen.insert(nearest);
for neighbour in neighbours(nearest, target) {
if !seen.contains(&neighbour) && !heap.contains(&neighbour) {
heap.push(neighbour);
let risk = distance.get(&nearest).unwrap() + map.get(&neighbour).unwrap();
if risk < *distance.get(&neighbour).unwrap_or(&u32::MAX) {
distance.insert(neighbour, risk);
for (next, weight) in &graph[new] {
match ans.get(next) {
// if ans[next] is a lower dist than the alternative one, we do nothing
Some(Some((_, dist_next))) if dist_new + *weight >= *dist_next => {}
// if ans[next] is None then next is start and so the distance won't be changed, it won't be added again in prio
Some(None) => {}
// the new path is shorter, either new was not in ans or it was farther
_ => {
ans.insert(*next, Some((*new, *weight + dist_new)));
prio.push(Reverse((*weight + dist_new, next, new)));
}
}
}
}
*distance.get(&target).unwrap()
ans.get(end).unwrap().clone()
}
fn add_edge(graph: &mut Graph<Coordinate, u32>, source: Coordinate, target: Coordinate, value: u32) {
graph.entry(source).or_insert_with(BTreeMap::new).insert(target, value);
graph.entry(target).or_insert_with(BTreeMap::new);
}
fn map_to_graph(map: &HashMap<Coordinate, u32>, end: Coordinate) -> Graph<Coordinate, u32> {
let mut g = BTreeMap::new();
for y in 0..=end.1 {
for x in 0..=end.0 {
for neighbour in neighbours((x, y), end) {
add_edge(&mut g, (x, y), neighbour, *map.get(&neighbour).unwrap())
}
}
}
g
}
#[cfg(test)]
@ -120,17 +157,17 @@ mod tests {
}
// Woo slow and i again don't feel like fixing it :p
// #[test]
// fn part1_real() -> anyhow::Result<()> {
// let d = Day15::init(crate::load_input("15")?)?;
// assert_eq!("388", d.part1()?);
// Ok(())
// }
//
// #[test]
// fn part2_real() -> anyhow::Result<()> {
// let d = Day15::init(crate::load_input("15")?)?;
// assert_eq!("2819", d.part2()?);
// Ok(())
// }
#[test]
fn part1_real() -> anyhow::Result<()> {
let d = Day15::init(crate::load_input("15")?)?;
assert_eq!("388", d.part1()?);
Ok(())
}
#[test]
fn part2_real() -> anyhow::Result<()> {
let d = Day15::init(crate::load_input("15")?)?;
assert_eq!("2819", d.part2()?);
Ok(())
}
}