112 lines
3.1 KiB
Rust
112 lines
3.1 KiB
Rust
use aoc_runner_derive::{aoc, aoc_generator};
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use grid::Grid;
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use itertools::Itertools;
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use std::io::BufRead;
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#[aoc_generator(day10)]
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pub fn get_input(input: &[u8]) -> TrailMap {
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TrailMap::from(input)
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}
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pub struct TrailMap {
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map: Grid<u8>,
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}
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impl<T: BufRead> From<T> for TrailMap {
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fn from(input: T) -> Self {
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Self { map: input.into() }
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}
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}
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impl TrailMap {
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fn trailheads(&self) -> Vec<(i64, i64)> {
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self.map
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.data
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.iter()
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.enumerate()
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.filter(|(_, v)| **v == b'0')
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.map(|(i, _v)| self.map.coord(i as i64).unwrap())
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.collect_vec()
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}
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fn count_reachable_from(&self, pos: &(i64, i64), needle: u8, visited: &mut Grid<bool>) -> u64 {
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if visited.get(pos) == Some(&true) {
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return 0;
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} else {
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visited.set(pos, true);
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}
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let our_val = self.map.get(pos).unwrap();
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if *our_val == needle {
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return 1;
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}
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// adjacents that are +1
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[(-1, 0), (1, 0), (0, -1), (0, 1)] // left, right, up, down
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.iter()
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.map(|(x_ofs, y_ofs)| (pos.0 + x_ofs, pos.1 + y_ofs)) // get target position
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.map(|target_pos| (target_pos, self.map.get(&target_pos))) // get value at that position
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.filter(|(_, val)| *val == Some(&(our_val + 1))) // only interested if it's our value + 1
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.map(|(pos, _)| pos) // discard the value
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.map(|pos| self.count_reachable_from(&pos, needle, visited))
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.sum()
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}
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fn count_paths_to(&self, pos: &(i64, i64), needle: u8) -> u64 {
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let our_val = self.map.get(pos).unwrap();
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if *our_val == needle {
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return 1;
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}
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[(-1, 0), (1, 0), (0, -1), (0, 1)] // left, right, up, down
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.iter()
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.map(|(x_ofs, y_ofs)| (pos.0 + x_ofs, pos.1 + y_ofs)) // get target position
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.map(|target_pos| (target_pos, self.map.get(&target_pos))) // get value at that position
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.filter(|(_, val)| *val == Some(&(our_val + 1))) // only interested if it's our value + 1
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.map(|(pos, _)| pos) // discard the value
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.map(|mov| self.count_paths_to(&mov, needle))
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.sum::<u64>()
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}
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}
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// PROBLEM 1 solution
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#[aoc(day10, part1)]
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pub fn part1(map: &TrailMap) -> u64 {
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map.trailheads()
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.iter()
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.map(|pos| {
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let mut visited = Grid::with_shape(map.map.width(), map.map.height(), false);
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map.count_reachable_from(pos, b'9', &mut visited)
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})
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.sum()
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}
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// PROBLEM 2 solution
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#[aoc(day10, part2)]
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pub fn part2(map: &TrailMap) -> u64 {
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map.trailheads()
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.iter()
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.map(|pos| map.count_paths_to(pos, b'9'))
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.sum::<u64>()
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}
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#[cfg(test)]
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mod tests {
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use crate::day10::*;
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const EXAMPLE: &[u8] = b"89010123
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78121874
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87430965
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96549874
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45678903
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32019012
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01329801
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10456732";
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#[test]
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fn part1_example() {
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assert_eq!(part1(&get_input(EXAMPLE)), 36);
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}
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#[test]
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fn part2_example() {
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assert_eq!(part2(&get_input(EXAMPLE)), 81);
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}
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}
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