136 lines
3.5 KiB
Rust
136 lines
3.5 KiB
Rust
#![feature(test, try_blocks)]
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extern crate test;
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use aoc2023::{boilerplate, common::*};
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use fnv::FnvHashMap;
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use std::mem::transmute;
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const DAY: usize = 14;
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type Parsed = Vec<Vec<Tile>>;
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#[allow(dead_code)]
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#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
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#[repr(u8)]
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enum Tile {
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Round = b'O',
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Cube = b'#',
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Empty = b'.',
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}
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fn parse_input(raw: &str) -> Parsed {
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raw.lines().map(|l| unsafe { transmute::<&str, &[Tile]>(l) }.to_vec()).collect()
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}
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fn tilt_north(grid: &mut Parsed) {
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for y in 0..grid.len() {
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for x in 0..grid[y].len() {
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if grid[y][x] == Tile::Round {
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let mut i = 0;
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while let Some(Tile::Empty) = try { grid.get(y.checked_sub(i + 1)?)?[x] } {
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i += 1;
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}
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grid[y][x] = Tile::Empty;
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grid[y - i][x] = Tile::Round;
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}
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}
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}
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}
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fn tilt_west(grid: &mut Parsed) {
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for line in grid.iter_mut() {
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for x in 0..line.len() {
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if line[x] == Tile::Round {
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let mut i = 0;
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while let Some(Tile::Empty) = try { line[x.checked_sub(i + 1)?] } {
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i += 1;
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}
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line[x] = Tile::Empty;
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line[x - i] = Tile::Round;
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}
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}
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}
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}
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fn tilt_south(grid: &mut Parsed) {
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for y in (0..grid.len()).rev() {
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for x in 0..(grid[y].len()) {
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if grid[y][x] == Tile::Round {
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let mut i = 0;
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while let Some(Tile::Empty) = try { grid.get(y + i + 1)?[x] } {
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i += 1;
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}
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grid[y][x] = Tile::Empty;
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grid[y + i][x] = Tile::Round;
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}
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}
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}
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}
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fn tilt_east(grid: &mut Parsed) {
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for line in grid.iter_mut() {
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for x in (0..line.len()).rev() {
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if line[x] == Tile::Round {
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let mut i = 0;
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while let Some(Tile::Empty) = try { line.get(x + i + 1)? } {
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i += 1;
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}
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line[x] = Tile::Empty;
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line[x + i] = Tile::Round;
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}
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}
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}
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}
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fn weight(grid: &Parsed) -> usize {
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grid.iter().rev().zip(1..).map(|(row, weight)| row.iter().filter(|&&t| t == Tile::Round).count() * weight).sum()
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}
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fn part1(parsed: &Parsed) -> usize {
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let mut grid = parsed.clone();
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tilt_north(&mut grid);
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weight(&grid)
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}
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fn part2(parsed: &Parsed) -> usize {
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let mut grid = parsed.clone();
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let mut grids = FnvHashMap::default();
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let mut n = 0;
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let cycle = loop {
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// I tried not cloning the grid and instead inserting only a grid hash and the weight here,
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// but that’s only ~15% faster and ugly, so we’ll just do it naively here.
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if let Some(old_n) = grids.insert(grid.clone(), n) {
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break n - old_n;
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}
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n += 1;
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tilt_north(&mut grid);
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tilt_west(&mut grid);
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tilt_south(&mut grid);
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tilt_east(&mut grid);
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};
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const REPETITIONS: usize = 1000000000;
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let steps = (REPETITIONS - n) % cycle;
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let cycle_start = n - cycle;
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grids.into_iter().find_map(|(g, n2)| (n2 == cycle_start + steps).then(|| weight(&g))).unwrap()
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}
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boilerplate! {
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TEST_INPUT == "\
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O....#....
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O.OO#....#
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.....##...
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OO.#O....O
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.O.....O#.
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O.#..O.#.#
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..O..#O..O
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.......O..
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#....###..
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#OO..#...."
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for tests: {
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part1: { TEST_INPUT => 136 },
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part2: { TEST_INPUT => 64 },
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},
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bench1 == 110407,
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bench2 == 87273,
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bench_parse: Vec::len => 100,
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}
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