diff --git a/2017/12/src/main.rs b/2017/12/src/main.rs
index 6d3f037..27c3eaa 100644
--- a/2017/12/src/main.rs
+++ b/2017/12/src/main.rs
@@ -1,14 +1,18 @@
-use std::io::{self, Read};
 use std::collections::{HashMap, HashSet};
-
+use std::io::{self, Read};
 
 fn parse(input: &str) -> (usize, Vec<usize>) {
     let parts = input.split("<->").collect::<Vec<_>>();
 
-    let from = parts[0].trim().parse::<usize>()
+    let from = parts[0]
+        .trim()
+        .parse::<usize>()
         .expect("faild to parse from");
 
-    let to = parts[1].split(',').filter_map(|to| to.trim().parse::<usize>().ok()).collect::<Vec<_>>();
+    let to = parts[1]
+        .split(',')
+        .filter_map(|to| to.trim().parse::<usize>().ok())
+        .collect::<Vec<_>>();
 
     (from, to)
 }
@@ -16,59 +20,61 @@ fn parse(input: &str) -> (usize, Vec<usize>) {
 fn main() {
     let mut input = String::new();
 
-    io::stdin().read_to_string(&mut input)
+    io::stdin()
+        .read_to_string(&mut input)
         .expect("faild to read input");
 
-    let pipes = input.lines().filter(|line| !line.is_empty()).map(parse).collect::<Vec<_>>();
+    let pipes = input
+        .lines()
+        .filter(|line| !line.is_empty())
+        .map(parse)
+        .collect::<HashMap<usize, Vec<_>>>();
 
-    let mut groups = HashMap::new();
+    let mut groups = Vec::new();
+    let mut visited = HashSet::new();
 
-    groups.entry(0).or_insert_with(HashSet::new).insert(0);
-
-    loop {
-        let mut done = true;
-
-        pipes.iter().for_each(|&(from, ref to)| {
-            let mut create = true;
-
-            for group in groups.values_mut() {
-                if group.contains(&from) {
-                    create = false;
-
-                    for id in to {
-                        if group.insert(*id) {
-                            done = false;
-                        }
-                    }
-                }
-            }
-
-            if create {
-                let group = groups.entry(from).or_insert_with(HashSet::new);
-
-                group.insert(from);
-
-                for id in to {
-                    group.insert(*id);
-                }
-            }
-        });
-
-        if done {
-            break;
+    for (to, from) in &pipes {
+        if visited.contains(&to) {
+            continue;
         }
+
+        let mut group = HashSet::new();
+        let mut visit = Vec::new();
+
+        group.insert(to);
+        visited.insert(to);
+
+        for id in from {
+            visit.push(id);
+        }
+
+        while let Some(id) = visit.pop() {
+            group.insert(id);
+            visited.insert(id);
+
+            for id in pipes.get(&id).unwrap() {
+                if !group.contains(&id) {
+                    visit.push(id);
+                }
+            }
+        }
+
+        groups.push(group);
     }
 
-    println!("part_one={}", groups[&0].len());
-    println!("part_two={}", groups.len());
-}
+    let group_0 = groups
+        .iter()
+        .find(|group| group.contains(&0))
+        .expect("found no group");
 
+    println!("part.one={}", group_0.len());
+    println!("part.two={}", groups.len());
+}
 
 #[cfg(test)]
 mod tests {
     use super::*;
 
-
     #[test]
     fn test_parse() {
         assert_eq!(parse("0 <-> 2"), (0, vec![2]));