1 files changed, 53 insertions, 0 deletions
diff --git a/2017/src/bin/day12.rs b/2017/src/bin/day12.rs
new file mode 100644
index 0000000..b133ba6
--- /dev/null
+++ b/2017/src/bin/day12.rs
@@ -0,0 +1,53 @@
+use std::collections::{HashMap, HashSet};
+use std::io::{self, Read};
+
+fn solve1(input: &str) -> usize {
+    let mut pipes: HashMap<u32, Vec<u32>> = HashMap::new();
+    for line in input.lines() {
+        let mut words = line.split_whitespace();
+        let src = words.next().unwrap().parse().unwrap();
+        assert_eq!(Some("<->"), words.next());
+        for dest in words {
+            let dest = dest.trim_right_matches(',').parse().unwrap();
+            pipes.entry(src).or_insert(vec![]).push(dest);
+            pipes.entry(dest).or_insert(vec![]).push(src);
+        }
+    }
+
+    let mut group = HashSet::new();
+    group.insert(0);
+
+    let mut prev = None;
+    while Some(group.len()) != prev {
+        prev = Some(group.len());
+        for (src, dests) in &pipes {
+            if group.contains(src) {
+                group.extend(dests);
+            }
+        }
+    }
+
+    group.len()
+}
+
+fn main() {
+    let mut input = String::new();
+    io::stdin().read_to_string(&mut input).unwrap();
+
+    println!("Part 1: {}", solve1(&input));
+}
+
+#[test]
+fn part1() {
+    assert_eq!(6, solve1(
+"\
+0 <-> 2
+1 <-> 1
+2 <-> 0, 3, 4
+3 <-> 2, 4
+4 <-> 2, 3, 6
+5 <-> 6
+6 <-> 4, 5
+"
+    ));
+}