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| 1 | +#![feature(test)] |
| 2 | + |
| 3 | +use advent_lib::direction::Direction; |
| 4 | +use advent_lib::geometry::{point2, vector2, Vector}; |
| 5 | +use advent_lib::{ |
| 6 | + direction::CardinalDirection, |
| 7 | + grid::{Grid, Location}, |
| 8 | + *, |
| 9 | +}; |
| 10 | +use advent_macros::FromRepr; |
| 11 | +use fxhash::FxHashMap; |
| 12 | +use std::cmp::{max, min}; |
| 13 | + |
| 14 | +#[repr(u8)] |
| 15 | +#[derive(FromRepr, PartialEq, Copy, Clone, Default)] |
| 16 | +enum Ground { |
| 17 | + #[default] |
| 18 | + Empty = b'.', |
| 19 | + Elf = b'#', |
| 20 | +} |
| 21 | + |
| 22 | +type Elfs = Grid<Ground>; |
| 23 | + |
| 24 | +fn prepare(grid: Grid<Ground>) -> Elfs { |
| 25 | + let mut elfs = Grid::new_empty(grid.width() * 3, grid.height() * 3); |
| 26 | + let offset = vector2(grid.width(), grid.height()); |
| 27 | + for (loc, ground) in grid.entries() { |
| 28 | + if let Some(target) = elfs.get_mut(loc + offset) { |
| 29 | + *target = *ground; |
| 30 | + } |
| 31 | + } |
| 32 | + elfs |
| 33 | +} |
| 34 | + |
| 35 | +const DIRECTIONS: [(Direction, [usize; 3]); 4] = [ |
| 36 | + (Direction::North, [7, 0, 1]), |
| 37 | + (Direction::South, [3, 4, 5]), |
| 38 | + (Direction::West, [5, 6, 7]), |
| 39 | + (Direction::East, [1, 2, 3]), |
| 40 | +]; |
| 41 | + |
| 42 | +fn find_possible_move(round: usize, has_elfs: [bool; 8]) -> Option<Direction> { |
| 43 | + for ix in 0..4 { |
| 44 | + let (dir, ixs) = DIRECTIONS[(round + ix) % 4]; |
| 45 | + if ixs.iter().all(|&ix| !has_elfs[ix]) { |
| 46 | + return Some(dir); |
| 47 | + } |
| 48 | + } |
| 49 | + None |
| 50 | +} |
| 51 | + |
| 52 | +fn step(elfs: &mut Elfs, round: usize) -> bool { |
| 53 | + let mut proposals = Vec::<(Location, Location)>::with_capacity(elfs.len()); |
| 54 | + let mut proposal_count = FxHashMap::with_capacity_and_hasher(elfs.len(), Default::default()); |
| 55 | + elfs.entries().filter(|&(_, g)| g == &Ground::Elf).for_each(|(loc, _)| { |
| 56 | + let has_elfs = CardinalDirection::ALL.map(|dir| elfs.get(loc + dir) == Some(&Ground::Elf)); |
| 57 | + if has_elfs.iter().any(|&has_elf| has_elf) { |
| 58 | + if let Some(dir) = find_possible_move(round, has_elfs) { |
| 59 | + let target = loc + dir; |
| 60 | + proposals.push((loc, target)); |
| 61 | + *proposal_count.entry(target).or_default() += 1; |
| 62 | + } |
| 63 | + } |
| 64 | + }); |
| 65 | + |
| 66 | + let mut some_change = false; |
| 67 | + for &(current, target) in proposals.iter() { |
| 68 | + if proposal_count.get(&target) == Some(&1) { |
| 69 | + if let Some(ground) = elfs.get_mut(current) { |
| 70 | + *ground = Ground::Empty |
| 71 | + } |
| 72 | + if let Some(ground) = elfs.get_mut(target) { |
| 73 | + *ground = Ground::Elf |
| 74 | + } |
| 75 | + some_change = true; |
| 76 | + } |
| 77 | + } |
| 78 | + |
| 79 | + some_change |
| 80 | +} |
| 81 | + |
| 82 | +fn get_range(elfs: &Elfs) -> (Vector<2, i32>, Vector<2, i32>) { |
| 83 | + let middle = vector2(elfs.width() / 2, elfs.height() / 2); |
| 84 | + elfs.entries().filter(|&(_, ground)| ground == &Ground::Elf).fold( |
| 85 | + (middle, middle), |
| 86 | + |(low, high), (curr, _)| { |
| 87 | + ( |
| 88 | + vector2(min(low.x(), curr.x()), min(low.y(), curr.y())), |
| 89 | + vector2(max(high.x(), curr.x()), max(high.y(), curr.y())), |
| 90 | + ) |
| 91 | + }, |
| 92 | + ) |
| 93 | +} |
| 94 | + |
| 95 | +fn empty_fields(elfs: &Elfs) -> i32 { |
| 96 | + let (min, max) = get_range(elfs); |
| 97 | + let mut count = 0; |
| 98 | + for y in min.y()..=max.y() { |
| 99 | + for x in min.x()..=max.x() { |
| 100 | + if elfs.get(point2(x, y)) == Some(&Ground::Empty) { |
| 101 | + count += 1; |
| 102 | + } |
| 103 | + } |
| 104 | + } |
| 105 | + count |
| 106 | +} |
| 107 | + |
| 108 | +fn calculate_part1(elfs: &Elfs) -> i32 { |
| 109 | + let mut elfs = elfs.clone(); |
| 110 | + for round in 0..10 { |
| 111 | + step(&mut elfs, round); |
| 112 | + } |
| 113 | + empty_fields(&elfs) |
| 114 | +} |
| 115 | + |
| 116 | +fn calculate_part2(elfs: &Elfs) -> usize { |
| 117 | + let mut elfs = elfs.clone(); |
| 118 | + for round in 0.. { |
| 119 | + let change = step(&mut elfs, round); |
| 120 | + if !change { |
| 121 | + return round + 1; |
| 122 | + } |
| 123 | + } |
| 124 | + 0 |
| 125 | +} |
| 126 | + |
| 127 | +day_main!(prepare => calculate_part1, calculate_part2); |
| 128 | +day_test!(23, example => 110, 20 ; crate::prepare ); |
| 129 | +day_test!(23 => 3762 ; crate::prepare ); // Part 2 is 997 but takes 5 seconds in test mode |
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