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day12.rs
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day12.rs
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//! # Digital Plumber
//!
//! This problem is the classic [union-find](https://en.wikipedia.org/wiki/Disjoint-set_data_structure).
//! A variant of [flood fill](https://en.wikipedia.org/wiki/Flood_fill) is used to find the
//! connected groups or cliques.
//!
//! For each program we [depth first search](https://en.wikipedia.org/wiki/Depth-first_search)
//! from each of its neighbors that we have not already visited. If a neighbor has been visited
//! then it must be either already in this clique or in another clique.
use crate::util::parse::*;
pub fn parse(input: &str) -> Vec<u32> {
let lines: Vec<_> = input.lines().collect();
let size = lines.len();
let mut visited = vec![false; size];
let mut groups = Vec::new();
for start in 0..size {
// DFS from each unvisited program.
if !visited[start] {
visited[start] = true;
let size = dfs(&lines, &mut visited, start);
groups.push(size);
}
}
groups
}
pub fn part1(input: &[u32]) -> u32 {
input[0]
}
pub fn part2(input: &[u32]) -> usize {
input.len()
}
fn dfs(lines: &[&str], visited: &mut [bool], index: usize) -> u32 {
let mut size = 1;
// At least the first 6 characters of each line can be skipped as it only contains the index
// that we already know.
for next in (&lines[index][6..]).iter_unsigned::<usize>() {
if !visited[next] {
visited[next] = true;
size += dfs(lines, visited, next);
}
}
size
}