feat: added day 23 part 1 and 2

Signed-off-by: Louis Vallat <contact@louis-vallat.dev>

.gitea/workflows/build_and_run.yml

@@ -11,7 +11,7 @@ jobs:
     name: Challenge for day
     strategy:
       matrix:
-        day_number: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22]
+        day_number: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23]
     runs-on: rust-bookworm
     steps:
       - name: Check out repository code

day23/Cargo.toml

@@ -0,0 +1,6 @@
+[package]
+name = "day23"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]

day23/src/main.rs

@@ -0,0 +1,94 @@
+use std::collections::{HashMap, HashSet};
+use std::{env, fs};
+
+fn read_input(path: &str) -> String {
+    fs::read_to_string(path).expect("Cannot read file.")
+}
+
+fn parse_input(input: &str) -> HashMap<&str, HashSet<&str>> {
+    let mut network = HashMap::new();
+    for connection in input.lines().filter(|l| !l.is_empty()) {
+        let pair = connection.split_once('-').unwrap();
+        network
+            .entry(pair.0)
+            .or_insert(HashSet::new())
+            .insert(pair.1);
+        network
+            .entry(pair.1)
+            .or_insert(HashSet::new())
+            .insert(pair.0);
+    }
+
+    network
+}
+
+fn part_1(network: &HashMap<&str, HashSet<&str>>) -> usize {
+    let mut triplets = HashSet::new();
+    let mut seen = HashSet::new();
+    for a in network.keys() {
+        for b in network.keys() {
+            let connections = network.get(a).unwrap();
+            if a == b
+                || !connections.contains(b)
+                || !(a.starts_with("t") || b.starts_with("t"))
+                || seen.contains(&(a, b))
+                || seen.contains(&(b, a))
+            {
+                continue;
+            }
+            seen.insert((a, b));
+
+            for common in connections.intersection(network.get(b).unwrap()) {
+                let mut triplet = vec![a, b, common];
+                triplet.sort();
+                triplets.insert(triplet);
+            }
+        }
+    }
+
+    triplets.len()
+}
+
+fn bron_kerbosch<'a>(
+    r: HashSet<&'a str>,
+    mut p: HashSet<&'a str>,
+    network: &HashMap<&'a str, HashSet<&'a str>>,
+) -> Vec<&'a str> {
+    if p.is_empty() {
+        return r.iter().copied().collect();
+    }
+
+    let mut clique = Vec::new();
+    for computer in p.clone() {
+        let connections = network.get(computer).unwrap();
+        let res = bron_kerbosch(
+            r.union(&HashSet::from([computer])).copied().collect(),
+            p.intersection(connections).copied().collect(),
+            network,
+        );
+        if res.len() > clique.len() {
+            clique = res;
+        }
+        p.remove(computer);
+    }
+
+    clique
+}
+
+fn part_2(network: &HashMap<&str, HashSet<&str>>) -> String {
+    let mut best_clique =
+        bron_kerbosch(HashSet::new(), network.keys().copied().collect(), &network);
+    best_clique.sort();
+    best_clique.join(",")
+}
+
+fn main() {
+    let args: Vec<String> = env::args().collect();
+    for arg in args.iter().skip(1) {
+        let input = read_input(&arg);
+        let network = parse_input(&input);
+        println!("[{}]", &arg);
+        println!("\t[Part 1] => Answer is '{}'.", part_1(&network));
+        println!("\t[Part 2] => Answer is '{}'.", part_2(&network));
+    }
+}