From 12fde697d3dda85a9c78af51bc8a7e377e5ea5f2 Mon Sep 17 00:00:00 2001
From: sepia <soerxpso@gmail.com>
Date: Mon, 23 Dec 2024 18:09:59 -0600
Subject: [PATCH] Day 23

---
 src/day23.rs | 93 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 src/main.rs  |  4 ++-
 2 files changed, 96 insertions(+), 1 deletion(-)
 create mode 100644 src/day23.rs

diff --git a/src/day23.rs b/src/day23.rs
new file mode 100644
index 0000000..38dfb20
--- /dev/null
+++ b/src/day23.rs
@@ -0,0 +1,93 @@
+use itertools::Itertools;
+use std::{
+    collections::{HashMap, HashSet},
+    fmt::{Display, Write},
+};
+
+#[derive(Copy, Clone, Eq, PartialEq, Hash, Debug, Ord, PartialOrd)]
+struct Computer(char, char);
+
+pub fn day23() {
+    let input_connections: Vec<(Computer, Computer)> = parse_input(&crate::input(23));
+    let connections = {
+        let mut connections: HashMap<Computer, Vec<Computer>> = HashMap::new();
+        for &(a, b) in input_connections.iter() {
+            connections.entry(a).or_insert(vec![]).push(b);
+            connections.entry(b).or_insert(vec![]).push(a);
+        }
+        connections
+    };
+
+    fn collect_cliques(
+        connections: &HashMap<Computer, Vec<Computer>>,
+        clique: &Vec<Computer>,
+        visited: &mut HashSet<Vec<Computer>>,
+    ) -> Vec<Vec<Computer>> {
+        let mut bigger_cliques: Vec<Vec<Computer>> = vec![];
+        bigger_cliques.push(clique.clone());
+        for (computer, friends) in connections.iter() {
+            if clique.contains(computer) {
+                continue;
+            }
+            if clique.iter().all(|groupie| friends.contains(groupie)) {
+                let mut new_clique = clique.clone();
+                new_clique.push(*computer);
+                new_clique.sort();
+                if visited.contains(&new_clique) {
+                    continue;
+                } else {
+                    visited.insert(new_clique.clone());
+                }
+                let mut new_bigger_cliques = collect_cliques(connections, &new_clique, visited);
+                bigger_cliques.append(&mut new_bigger_cliques);
+            }
+        }
+        bigger_cliques
+    }
+    let mut visited = HashSet::new();
+    let mut all_cliques: Vec<Vec<Computer>> = connections
+        .keys()
+        .map(|&c| vec![c])
+        .flat_map(|seed| collect_cliques(&connections, &seed, &mut visited))
+        .collect();
+    all_cliques.sort_by_key(|group| group.len());
+    let mut maximum_clique = all_cliques.last().unwrap().clone();
+    println!("The biggest clique's size is {}.", maximum_clique.len());
+    maximum_clique.sort();
+    println!(
+        "The biggest clique's password is {}",
+        maximum_clique.iter().map(|c| format!("{c}")).join(",")
+    );
+
+    let t_trios = all_cliques
+        .iter()
+        .filter(|clique| clique.len() == 3)
+        .filter(|trio| trio.iter().any(|c| c.0 == 't'))
+        .count();
+    println!("{t_trios} trios contain a friend who starts with t.");
+}
+
+impl Computer {
+    fn from_string(s: &str) -> Self {
+        Self(s.chars().nth(0).unwrap(), s.chars().nth(1).unwrap())
+    }
+}
+
+impl Display for Computer {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.write_char(self.0)?;
+        f.write_char(self.1)
+    }
+}
+
+fn parse_input(input: &str) -> Vec<(Computer, Computer)> {
+    input
+        .lines()
+        .map(|line| {
+            line.split("-")
+                .map(Computer::from_string)
+                .collect_tuple()
+                .unwrap()
+        })
+        .collect()
+}
diff --git a/src/main.rs b/src/main.rs
index 604b8e5..4a784e0 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -28,7 +28,9 @@ mod day2;
 mod day20;
 #[allow(dead_code)]
 mod day21;
+#[allow(dead_code)]
 mod day22;
+mod day23;
 #[allow(dead_code)]
 mod day3;
 #[allow(dead_code)]
@@ -45,7 +47,7 @@ mod day8;
 mod day9;
 
 fn main() {
-    day22::day22();
+    day23::day23();
 }
 
 pub fn input(day: u8) -> String {