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use std::collections::{HashMap, HashSet};
static DAY: u8 = 12;
fn main() {
let input = advent::read_lines(DAY);
println!("{DAY}a: {}", fencing_price(&input));
println!("{DAY}b: {}", 0);
}
#[derive(Eq, PartialEq, Copy, Clone, Hash)]
struct Position {
x: isize,
y: isize,
}
fn count_fences(region: &HashSet<Position>) -> usize {
let mut total_fences = 0;
for pos in region {
/* every plot has 4 fences, except it has neighbors of the same type */
let mut fences = 4;
for diff in [(-1, 0), (1, 0), (0, -1), (0, 1)] {
let neighbor = Position { x: pos.x + diff.0, y: pos.y + diff.1 };
if region.contains(&neighbor) {
fences -= 1;
}
}
total_fences += fences;
}
total_fences
}
fn find_region(plots: &HashMap<Position, char>, pos: Position, visited: &mut HashSet<Position>) -> HashSet<Position> {
let mut region = HashSet::new();
if visited.contains(&pos) {
return region;
}
let plot_type = plots.get(&pos).unwrap();
region.insert(pos);
visited.insert(pos);
for diff in [(-1, 0), (1, 0), (0, -1), (0, 1)] {
let neighbor = Position { x: pos.x + diff.0, y: pos.y + diff.1 };
if let Some(t) = plots.get(&neighbor) {
if t == plot_type {
for r in find_region(plots, neighbor, visited) {
region.insert(r);
}
}
}
}
region
}
fn find_regions(plots: &HashMap<Position, char>) -> HashMap<char, Vec<HashSet<Position>>> {
let mut regions = HashMap::new();
let mut visited = HashSet::new();
for (pos, c) in plots {
if visited.contains(pos) {
continue;
}
let region = find_region(plots, *pos, &mut HashSet::new());
for plot in ®ion {
visited.insert(*plot);
}
regions.entry(*c).or_insert(Vec::new()).push(region);
}
regions
}
fn fencing_price(input: &[String]) -> usize {
let mut plots = HashMap::new();
for (x, line) in input.iter().enumerate() {
for (y, c) in line.chars().enumerate() {
let pos = Position { x: x as isize, y: y as isize };
plots.insert(pos, c);
}
}
let all_regions = find_regions(&plots);
let mut total_price = 0;
for regions in all_regions.values() {
for region in regions {
let area = region.len();
let fences = count_fences(region);
total_price += area * fences;
}
}
total_price
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test() {
let input = [
"AAAA",
"BBCD",
"BBCC",
"EEEC",
].iter().map(|&x| String::from(x)).collect::<Vec<_>>();
assert_eq!(fencing_price(&input), 140);
let input = [
"OOOOO",
"OXOXO",
"OOOOO",
"OXOXO",
"OOOOO",
].iter().map(|&x| String::from(x)).collect::<Vec<_>>();
assert_eq!(fencing_price(&input), 772);
let input = [
"RRRRIICCFF",
"RRRRIICCCF",
"VVRRRCCFFF",
"VVRCCCJFFF",
"VVVVCJJCFE",
"VVIVCCJJEE",
"VVIIICJJEE",
"MIIIIIJJEE",
"MIIISIJEEE",
"MMMISSJEEE",
].iter().map(|&x| String::from(x)).collect::<Vec<_>>();
assert_eq!(fencing_price(&input), 1930);
}
}
|
