day17: problem 1 solution - a messy one!
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297
17/src/main.rs
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297
17/src/main.rs
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use std::collections::hash_map::RandomState;
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use std::collections::{BinaryHeap, HashMap};
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use std::fmt::{Display, Write};
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use std::fs::File;
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use std::io::{BufRead, BufReader, Lines};
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use std::iter::repeat;
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use std::time::Instant;
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use petgraph::algo::dijkstra;
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use petgraph::prelude::*;
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// BOILERPLATE
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type InputIter = Lines<BufReader<File>>;
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fn get_input() -> InputIter {
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let f = File::open("input").unwrap();
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let br = BufReader::new(f);
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br.lines()
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}
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fn main() {
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let start = Instant::now();
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let ans1 = problem1(get_input());
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let duration = start.elapsed();
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println!("Problem 1 solution: {} [{}s]", ans1, duration.as_secs_f64());
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let start = Instant::now();
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let ans2 = problem2(get_input());
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let duration = start.elapsed();
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println!("Problem 2 solution: {} [{}s]", ans2, duration.as_secs_f64());
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}
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// PARSE
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#[derive(Clone, Copy, PartialEq, Eq, Debug, Hash)]
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enum Direction {
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Left,
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Right,
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Up,
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Down,
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}
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impl Direction {
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const fn all() -> &'static [Self; 4] {
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&[
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Direction::Left,
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Direction::Right,
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Direction::Up,
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Direction::Down,
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]
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}
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const fn opposite(&self) -> Self {
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match self {
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Direction::Left => Direction::Right,
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Direction::Right => Direction::Left,
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Direction::Up => Direction::Down,
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Direction::Down => Direction::Up,
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}
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}
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}
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struct CityMap {
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map: Vec<Vec<u64>>,
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}
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impl CityMap {
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fn offset_pos(&self, pos: (usize, usize), dir: &Direction) -> Option<(usize, usize)> {
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match dir {
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Direction::Left if pos.0 > 0 => Some((pos.0 - 1, pos.1)),
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Direction::Right if pos.0 < self.map[0].len() - 1 => Some((pos.0 + 1, pos.1)),
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Direction::Up if pos.1 > 0 => Some((pos.0, pos.1 - 1)),
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Direction::Down if pos.1 < self.map.len() - 1 => Some((pos.0, pos.1 + 1)),
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_ => None,
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}
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}
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}
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type Position = (usize, usize);
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struct WalkCost<'a> {
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start: Position,
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cost_from: Vec<Vec<HashMap<(Direction, usize), u64>>>,
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dir_to: HashMap<Position, Direction>,
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map: &'a CityMap,
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}
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#[derive(Debug)]
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struct Move {
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new_pos: Position,
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dir: &'static Direction,
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consecutive: usize,
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weight: u64,
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}
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impl PartialEq for Move {
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fn eq(&self, other: &Self) -> bool {
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self.weight == other.weight
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}
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}
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impl Eq for Move {}
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impl PartialOrd for Move {
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fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
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Some(self.cmp(other))
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}
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}
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impl Ord for Move {
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fn cmp(&self, other: &Self) -> std::cmp::Ordering {
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std::cmp::Reverse(self.weight).cmp(&std::cmp::Reverse(other.weight))
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}
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}
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impl<'a> WalkCost<'a> {
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fn from_map(map: &'a CityMap, start: Position) -> Self {
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Self {
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map,
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start,
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cost_from: map
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.map
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.iter()
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.map(|row| repeat(HashMap::new()).take(row.len()).collect())
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.collect(),
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dir_to: HashMap::new(),
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}
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}
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fn compute(&mut self) {
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let mut unvisited_next_moves: BinaryHeap<Move> = BinaryHeap::new();
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let valid_start_moves: Vec<Move> = Direction::all()
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.iter()
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.filter_map(|dir| {
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self.map.offset_pos(self.start, dir).and_then(|pos| {
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Some(Move {
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new_pos: pos,
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dir,
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consecutive: 1,
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weight: self.map.map[pos.1][pos.0],
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})
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})
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}) // valid positions
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.collect();
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for m in valid_start_moves {
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unvisited_next_moves.push(m);
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}
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while let Some(cur_move) = unvisited_next_moves.pop() {
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// we've been here already at a lower cost
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// if cur_move.weight >= self.cost_to[cur_move.new_pos.1][cur_move.new_pos.0] {
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// continue;
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// }
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if let Some(last_weight) = self.cost_from[cur_move.new_pos.1][cur_move.new_pos.0].get(&(*cur_move.dir, cur_move.consecutive)) {
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if cur_move.weight < *last_weight {
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self.cost_from[cur_move.new_pos.1][cur_move.new_pos.0].insert((*cur_move.dir, cur_move.consecutive), cur_move.weight);
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} else { continue; }// visited before at lower cost }
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} else {
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self.cost_from[cur_move.new_pos.1][cur_move.new_pos.0].insert((*cur_move.dir, cur_move.consecutive), cur_move.weight);
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}
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// println!("state at {:?}: {:?}", cur_move, self.cost_from[cur_move.new_pos.1][cur_move.new_pos.0]);
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let valid_moves = Direction::all().iter().filter_map(|dir| {
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self.map
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.offset_pos(cur_move.new_pos, dir)
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.and_then(|new_pos| {
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Some(Move {
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new_pos,
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dir,
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consecutive: if cur_move.dir == dir {
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cur_move.consecutive + 1
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} else {
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1
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},
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weight: cur_move.weight + self.map.map[new_pos.1][new_pos.0],
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})
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})
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.filter(|m| m.consecutive != 4 && *m.dir != cur_move.dir.opposite())
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.filter(|m| {
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m.weight < *self.cost_from[m.new_pos.1][m.new_pos.0].get(&(*m.dir, m.consecutive)).unwrap_or(&u64::MAX)
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})
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}); // valid positions
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// println!("valid moves with {:?}", cur_move);
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for next_move in valid_moves {
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// println!(" {:?}", next_move);
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unvisited_next_moves.push(next_move);
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}
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}
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}
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fn shortest_path_to(&self, to: Position) -> Vec<(Position, Direction)> {
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let mut path = Vec::new();
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let mut cur_pos = to;
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// start at the end, walk backwards
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while cur_pos != self.start {
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let dir = self.dir_to.get(&cur_pos).unwrap();
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path.push((cur_pos, *dir));
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cur_pos = self.map.offset_pos(cur_pos, &dir.opposite()).unwrap();
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}
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path
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}
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fn print_shortest_path(&self, to: Position) {
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let path = self.shortest_path_to(to);
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let map: HashMap<_, _, RandomState> = HashMap::from_iter(path.into_iter());
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// for y in 0..self.cost_to.len() {
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// for x in 0..self.map.map[y].len() {
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// if let Some(to_dir) = map.get(&(x, y)) {
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// let c = match to_dir {
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// Direction::Left => '<',
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// Direction::Right => '>',
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// Direction::Up => '^',
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// Direction::Down => 'v',
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// };
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// print!("{}", c);
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// } else {
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// print!("{}", self.map.map[y][x]);
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// }
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// }
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// println!();
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// }
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}
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}
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impl<'a> Display for WalkCost<'a> {
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fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
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// for y in 0..self.cost_to.len() {
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// for cost in &self.cost_to[y] {
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// f.write_fmt(format_args!("{:3} ", cost))?;
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// }
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// f.write_str(" ")?;
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// for input in &self.map.map[y] {
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// f.write_fmt(format_args!("{:3} ", input))?;
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// }
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// writeln!(f)?;
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// }
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Ok(())
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}
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}
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impl<T: BufRead> From<Lines<T>> for CityMap {
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fn from(lines: Lines<T>) -> Self {
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Self {
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map: lines
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.map(|l| l.unwrap().chars().map(|c| c as u64 - '0' as u64).collect())
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.collect(),
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}
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}
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}
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// PROBLEM 1 solution
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fn problem1<T: BufRead>(input: Lines<T>) -> u64 {
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let map = CityMap::from(input);
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let mut costs = WalkCost::from_map(&map, (0, 0));
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costs.compute();
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println!("{}", costs);
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// costs.print_shortest_path((costs.cost_to[0].len() - 1, costs.cost_to.len() - 1));
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*costs.cost_from[costs.cost_from.len()-1][costs.cost_from[0].len() - 1].values().min().unwrap()
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}
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// PROBLEM 2 solution
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fn problem2<T: BufRead>(input: Lines<T>) -> u64 {
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0
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}
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#[cfg(test)]
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mod tests {
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use crate::*;
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use std::io::Cursor;
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const EXAMPLE: &str = &"2413432311323
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3215453535623
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3255245654254
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3446585845452
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4546657867536
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1438598798454
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4457876987766
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3637877979653
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4654967986887
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4564679986453
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1224686865563
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2546548887735
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4322674655533
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";
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#[test]
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fn problem1_example() {
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let c = Cursor::new(EXAMPLE);
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assert_eq!(problem1(c.lines()), 102);
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}
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#[test]
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fn problem2_example() {
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let c = Cursor::new(EXAMPLE);
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assert_eq!(problem2(c.lines()), 0);
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}
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}
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