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|
/// --- Part Two ---
///
/// As you walk up the hill, you suspect that the Elves will want to turn this into a hiking
/// trail. The beginning isn't very scenic, though; perhaps you can find a better starting point.
///
/// To maximize exercise while hiking, the trail should start as low as possible: elevation a. The
/// goal is still the square marked E. However, the trail should still be direct, taking the fewest
/// steps to reach its goal. So, you'll need to find the shortest path from any square at elevation
/// a to the square marked E.
///
/// Again consider the example from above:
///
/// ```
/// Sabqponm
/// abcryxxl
/// accszExk
/// acctuvwj
/// abdefghi
/// ```
///
/// Now, there are six choices for starting position (five marked a, plus the square marked S that
/// counts as being at elevation a). If you start at the bottom-left square, you can reach the goal
/// most quickly:
///
/// ```
/// ...v<<<<
/// ...vv<<^
/// ...v>E^^
/// .>v>>>^^
/// >^>>>>>^
/// ```
///
/// This path reaches the goal in only 29 steps, the fewest possible.
///
/// What is the fewest steps required to move starting from any square with elevation a to the
/// location that should get the best signal?
use clap::Parser;
use itertools::Itertools;
use pathfinding::prelude::bfs;
use std::fs::File;
use std::hash::{Hash, Hasher};
use std::io::prelude::*;
use std::io::BufReader;
use std::path::PathBuf;
const FILEPATH: &'static str = "examples/input.txt";
#[derive(Parser, Debug)]
#[clap(author, version, about, long_about = None)]
struct Cli {
#[clap(short, long, default_value = FILEPATH)]
file: PathBuf,
}
#[derive(Clone, Debug)]
struct Arena(Vec<Vec<Node>>);
#[derive(Copy, Clone, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
struct Pos(usize, usize);
#[derive(Clone, Debug)]
struct Node {
pos: Pos,
value: char,
connected: Vec<Pos>,
}
impl Node {
fn new(pos: Pos, value: char) -> Self {
Node {
pos,
value,
connected: Vec::new(),
}
}
}
impl PartialEq for Node {
fn eq(&self, other: &Self) -> bool {
self.pos == other.pos
}
}
impl Eq for Node {}
impl Hash for Node {
fn hash<H: Hasher>(&self, state: &mut H) {
self.pos.hash(state);
}
}
impl Arena {
fn get(&self, coords: Pos) -> &Node {
&self.0[coords.0][coords.1]
}
fn get_mut(&mut self, coords: Pos) -> &mut Node {
&mut self.0[coords.0][coords.1]
}
}
fn is_connected(x: char, y: char) -> bool {
let (x, y) = match (x, y) {
('S', _) => ('a', y),
('E', _) => ('z', y),
(_, 'S') => (x, 'a'),
(_, 'E') => (x, 'z'),
_ => (x, y),
};
let (x, y) = (x as i8, y as i8);
i8::abs(x - y) <= 1 || x > y
}
fn main() {
let args = Cli::parse();
let file = File::open(&args.file).unwrap();
let reader = BufReader::new(file);
let mut arena = Arena(Vec::new());
let _ = reader
.lines()
.enumerate()
.map(|(idx, l)| {
l.unwrap()
.chars()
.enumerate()
.map(|(idy, c)| Node::new(Pos(idx, idy), c))
.collect_vec()
})
.scan(&mut arena, |arena, row| {
arena.0.push(row);
Some(())
})
.last();
let xdim = arena.0.len();
let ydim = arena.0[0].len();
let mut lowest_pos = Vec::new();
let mut end_pos = None;
for idx in 0..xdim {
for idy in 0..ydim {
let node_val = arena.get(Pos(idx, idy)).value;
match node_val {
'a' | 'S' => lowest_pos.push(Pos(idx, idy)),
'E' => end_pos = Some(Pos(idx, idy)),
_ => (),
}
if idx != 0 {
let up_idx = Pos(idx - 1, idy);
if is_connected(node_val, arena.get(up_idx).value) {
arena.get_mut(Pos(idx, idy)).connected.push(up_idx);
}
}
if idx != xdim - 1 {
let down_idx = Pos(idx + 1, idy);
if is_connected(node_val, arena.get(down_idx).value) {
arena.get_mut(Pos(idx, idy)).connected.push(down_idx);
}
}
if idy != 0 {
let left_idx = Pos(idx, idy - 1);
if is_connected(node_val, arena.get(left_idx).value) {
arena.get_mut(Pos(idx, idy)).connected.push(left_idx);
}
}
if idy != ydim - 1 {
let right_idx = Pos(idx, idy + 1);
if is_connected(node_val, arena.get(right_idx).value) {
arena.get_mut(Pos(idx, idy)).connected.push(right_idx);
}
}
}
}
let end = arena.get(end_pos.unwrap());
let res = lowest_pos
.into_iter()
.filter_map(|s| {
let steps = bfs(
&arena.get(s),
|n| n.connected.iter().map(|&p| arena.get(p)),
|&n| n == end,
)?
.len()
- 1;
Some(steps)
})
.min()
.unwrap();
println!("{res}");
}
|
