89 lines
2.8 KiB
Rust
89 lines
2.8 KiB
Rust
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#![feature(let_chains)]
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use std::collections::{HashSet, VecDeque};
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const GRID_SIZE: usize = 140;
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fn dfs(grid: &[[char; GRID_SIZE]; GRID_SIZE], start: (usize, usize)) -> HashSet<(usize, usize)> {
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let mut queue = VecDeque::from([start]);
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let mut set = HashSet::from([start]);
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let plant_type = grid[start.0][start.1];
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while let Some(next) = queue.pop_front() {
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let to_check = [
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(next.0 + 1, next.1),
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(next.0.wrapping_sub(1), next.1),
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(next.0, next.1 + 1),
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(next.0, next.1.wrapping_sub(1)),
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];
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for pos in to_check {
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if set.contains(&pos) {
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continue;
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}
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if let Some(plant) = grid.get(pos.0).and_then(|r| r.get(pos.1))
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&& *plant == plant_type
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{
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queue.push_back(pos);
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set.insert(pos);
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}
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}
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}
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set
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}
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fn main() {
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let mut input_iter = include_str!("input.txt").lines().map(|l| {
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let mut iter = l.chars();
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std::array::from_fn::<_, GRID_SIZE, _>(|_| iter.next().unwrap())
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});
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let grid: [_; GRID_SIZE] = std::array::from_fn(|_| input_iter.next().unwrap());
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// Parse all independent regions
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let mut regions = Vec::<HashSet<(usize, usize)>>::new();
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for row in 0..GRID_SIZE {
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for col in 0..GRID_SIZE {
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if regions.iter().all(|region| !region.contains(&(row, col))) {
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regions.push(dfs(&grid, (row, col)));
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}
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}
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}
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// Sanity check -> are there any duplicated nodes between the regions?
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assert_eq!(
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regions.iter().map(|r| r.len()).sum::<usize>(),
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regions
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.iter()
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.flatten()
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.collect::<HashSet<&(usize, usize)>>()
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.len()
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);
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// Calculate area and perimeter of each
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let mut sum = 0;
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for region in regions.into_iter() {
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let area = region.len();
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let mut perimeter_set = Vec::<(Option<usize>, Option<usize>)>::new();
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for pos in region.iter() {
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// None in a position is a special case meaning "overfilled in the negative direction"
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// Since we don't actually access the point there, it just gets treated like -1 would
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let to_check = [
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(pos.0.checked_add(1), Some(pos.1)),
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(pos.0.checked_sub(1), Some(pos.1)),
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(Some(pos.0), pos.1.checked_add(1)),
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(Some(pos.0), pos.1.checked_sub(1)),
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];
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for outer_pos in to_check {
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if (outer_pos.0.is_none() || outer_pos.1.is_none())
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|| !region.contains(&(outer_pos.0.unwrap(), outer_pos.1.unwrap()))
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{
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perimeter_set.push(outer_pos);
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}
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}
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}
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sum += area * perimeter_set.len();
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}
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println!("Result: {sum}");
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}
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