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Rust
github codeberg gitlab
First tried a really slow brute force, but after waiting many minutes heard others talk of Karger's Algorithm, so I implemented that.
use rand::prelude::*; use std::collections::HashSet; type Graph = (V, E); type V = HashSet<String>; type E = Vec<(String, String)>; fn parse_input(input: &str) -> Graph { let mut vertices = HashSet::new(); let mut edges = Vec::new(); for line in input.trim().lines() { let mut it = line.split(':'); let left = it.next().unwrap(); vertices.insert(left.to_owned()); for right in it.next().unwrap().trim().split_whitespace() { vertices.insert(right.to_owned()); edges.push((left.to_owned(), right.to_owned())); } } (vertices, edges) } fn part1(input: &str) -> usize { let (vertices, edges) = parse_input(input); let mut rng = rand::thread_rng(); // Karger's Algorithm loop { let mut vertices = vertices.clone(); let mut edges = edges.clone(); while vertices.len() > 2 { let i = rng.gen_range(0..edges.len()); let (v1, v2) = edges[i].clone(); // contract the edge edges.swap_remove(i); vertices.remove(&v1); vertices.remove(&v2); let new_v = format!("{}:{}", v1, v2); vertices.insert(new_v.clone()); for (e1, e2) in edges.iter_mut() { if *e1 == v1 || *e1 == v2 { *e1 = new_v.clone() } if *e2 == v1 || *e2 == v2 { *e2 = new_v.clone() } } // remove loops let mut j = 0; while j < edges.len() { let (e1, e2) = &edges[j]; if e1 == e2 { edges.swap_remove(j); } else { j += 1; } } } if edges.len() == 3 { break vertices .iter() .map(|s| s.split(':').count()) .product::<usize>(); } } }