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use std::collections::{hash_map::Entry, BinaryHeap, HashMap, HashSet, VecDeque};
use anyhow::Context;
use crate::{Problem, Solution};
pub struct Day17;
impl Problem for Day17 {
const DAY: u8 = 17;
const INPUT: &'static str = include_str!("../input/day_17.txt");
}
impl Solution for Day17 {
type Answer1 = usize;
type Answer2 = usize;
fn part_1(input: &str) -> anyhow::Result<Self::Answer1> {
let grid = parse_grid(input).context("Failed to parse grid")?;
let path = astar(&grid, (0, 0), (grid.len() - 1, grid[0].len() - 1))
.context("Failed to find path")?;
let mut visited = HashSet::new();
for (p, cost) in path {
visited.insert(p);
println!("{p:?}: {cost}");
}
for (row, v) in grid.iter().enumerate() {
let mut output = String::new();
for (col, _) in v.iter().enumerate() {
if visited.contains(&(row, col)) {
output.push('#');
} else {
output.push('.');
}
}
println!("{output}")
}
todo!()
}
fn part_2(input: &str) -> anyhow::Result<Self::Answer2> {
todo!()
}
}
fn parse_grid(input: &str) -> Option<Grid> {
input
.lines()
.map(|v| {
v.chars()
.map(|c| c.to_digit(10).map(|n| n as usize))
.try_collect::<Vec<_>>()
})
.try_collect::<Grid>()
}
fn astar(grid: &Grid, start: Position, goal: Position) -> Option<Vec<(Position, usize)>> {
let mut queue = BinaryHeap::from([Node::start(start)]);
let mut cache = HashMap::from([(start, usize::MAX)]);
while let Some(node) = queue.pop() {
for next in node.successors(grid, goal) {
if next.position == goal {
return Some(rebuild_path(cache, next));
}
match cache.entry(next.position) {
Entry::Vacant(e) => {
e.insert(next.cost);
}
Entry::Occupied(mut e) => {
if next.cost < *e.get() {
e.insert(next.cost);
} else {
continue;
}
}
}
queue.push(next)
}
}
None
}
fn rebuild_path(cache: HashMap<Position, usize>, node: Node) -> Vec<(Position, usize)> {
let mut path = node
.parents
.into_iter()
.map(|p| (p, *cache.get(&p).unwrap()))
.collect::<Vec<_>>();
path.push((node.position, node.cost));
path
}
type Grid = Vec<Vec<usize>>;
type Position = (usize, usize);
#[derive(Debug, Default, Clone, PartialEq, Eq)]
struct Node {
estimated: usize,
cost: usize,
position: Position,
parents: Vec<Position>,
trail: VecDeque<Edge>,
}
impl Node {
fn start(position: Position) -> Self {
Node {
position,
estimated: usize::MAX,
..Default::default()
}
}
fn successors(&self, grid: &Grid, goal: Position) -> Vec<Self> {
Edge::ALL
.into_iter()
.filter(|e| self.trail.len() < 3 || !self.trail.iter().all(|t| e == t))
.inspect(|e| print!(" {e:?}"))
.filter_map(|e| {
let (row, col) = self.position;
let position = match e {
Edge::North if row < grid.len() - 1 => (row.checked_add(1)?, col),
Edge::East if col < grid[row].len() - 1 => (row, col.checked_add(1)?),
Edge::South => (row.checked_sub(1)?, col),
Edge::West => (row, col.checked_sub(1)?),
_ => return None,
};
let mut next = self.clone();
next.position = position;
next.cost += grid[position.0][position.1];
next.estimated = next.cost + next.dist(goal);
next.parents.push(self.position);
if next.trail.len() >= 3 {
next.trail.pop_front();
}
next.trail.push_back(e);
Some(next)
})
.collect()
}
fn dist(&self, p2: Position) -> usize {
self.position.0.abs_diff(p2.0) + self.position.1.abs_diff(p2.1)
}
}
impl PartialOrd for Node {
fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
Some(self.cmp(other))
}
}
impl Ord for Node {
fn cmp(&self, other: &Self) -> std::cmp::Ordering {
match self.estimated.cmp(&other.estimated) {
std::cmp::Ordering::Equal => self.cost.cmp(&other.cost),
c => c,
}
}
}
#[derive(Debug, Default, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
enum Edge {
North,
#[default]
East,
South,
West,
}
impl Edge {
const ALL: [Edge; 4] = [Edge::North, Edge::East, Edge::South, Edge::West];
}
#[cfg(test)]
mod tests {
use super::*;
const INPUT: &str = indoc::indoc! {r#"
2413432311323
3215453535623
3255245654254
3446585845452
4546657867536
1438598798454
4457876987766
3637877979653
4654967986887
4564679986453
1224686865563
2546548887735
4322674655533
"#};
#[test]
fn test_part_1() -> anyhow::Result<()> {
Ok(assert_eq!(102, Day17::part_1(INPUT)?))
}
}
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