103 lines
2.5 KiB
Rust
103 lines
2.5 KiB
Rust
use aoc_runner_derive::{aoc, aoc_generator};
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use grid::{Coord2d, Grid};
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use std::str::FromStr;
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#[aoc_generator(day7)]
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fn parse(input: &str) -> Grid<u8> {
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Grid::from_str(input).unwrap()
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}
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fn emit_beams(grid: &mut Grid<u8>, pos: Coord2d) -> u64 {
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match grid.set(&pos, b'|') {
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None | Some(b'|') => 0,
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Some(b'.') | Some(b'S') => emit_beams(grid, pos + &(0, 1)),
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Some(b'^') => 1 + emit_beams(grid, pos + &(-1, 0)) + emit_beams(grid, pos + &(1, 0)),
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_ => panic!(),
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}
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}
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#[aoc(day7, part1)]
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fn part1(input: &Grid<u8>) -> u64 {
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let mut grid = input.clone();
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emit_beams(&mut grid, input.find(&b'S').unwrap())
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}
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#[aoc(day7, part2)]
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fn part2(input: &Grid<u8>) -> u64 {
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let mut col_counts = vec![0; input.width()];
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col_counts[input.find(&b'S').unwrap().x as usize] = 1;
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// Start row is already set up
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for y in 1..input.height() {
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// for each column with non-zero counts
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for x in 0..input.width() {
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if col_counts[x] == 0 {
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continue;
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}
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match input.get(&(x, y)) {
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// if our current position is a caret, add that count to our neighbours
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Some(b'^') => {
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for col in [x as i64 - 1, x as i64 + 1]
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.into_iter()
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.filter(|x| *x >= 0 && *x < input.width() as i64)
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{
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col_counts[col as usize] += col_counts[x];
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}
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col_counts[x] = 0;
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}
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// if our current position is a . do nothing, it's already counted
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Some(b'.') => continue,
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Some(c) => panic!("unexpected character {c}"),
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None => panic!("How did we end up outside the grid?"),
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}
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}
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}
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col_counts.iter().sum::<u64>()
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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const TRIVIAL_EXAMPLE: &str = "...S...
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.......
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...^...
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..^.^.^
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...^.^.
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.......
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.......";
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const EXAMPLE: &str = ".......S.......
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...............
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.......^.......
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...............
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......^.^......
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...............
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.....^.^.^.....
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...............
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....^.^...^....
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...............
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...^.^...^.^...
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...............
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..^...^.....^..
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...............
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.^.^.^.^.^...^.
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...............";
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#[test]
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fn part1_example() {
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assert_eq!(part1(&parse(EXAMPLE)), 21);
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}
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#[test]
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fn part2_example() {
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assert_eq!(part2(&parse(EXAMPLE)), 40);
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}
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#[test]
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fn part2_trivial_example() {
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assert_eq!(part2(&parse(TRIVIAL_EXAMPLE)), 7);
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}
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}
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