1 files changed, 61 insertions, 0 deletions
diff --git a/2017/src/bin/day09.rs b/2017/src/bin/day09.rs
new file mode 100644
index 0000000..a8492d0
--- /dev/null
+++ b/2017/src/bin/day09.rs
@@ -0,0 +1,61 @@
+use std::io::{self, Read};
+
+#[derive(Debug, Clone, Copy)]
+enum State {
+    Group,
+    Garbage,
+    Ignore,
+}
+
+use self::State::*;
+
+#[derive(Debug, Clone, Copy)]
+struct Machine(State, u32);
+
+impl Machine {
+    fn next(self, input: char) -> Self {
+        match (self.0, input) {
+            (Ignore, _) => Machine(Garbage, self.1),
+            (Garbage, '!') => Machine(Ignore, self.1),
+            (Garbage, '>') => Machine(Group, self.1),
+            (Garbage, _) => self,
+            (Group, '<') => Machine(Garbage, self.1),
+            (Group, '{') => Machine(Group, self.1 + 1),
+            (Group, '}') => Machine(Group, self.1 - 1),
+            (Group, ',') => self,
+            _ => unimplemented!(),
+        }
+    }
+}
+
+fn solve1(input: &str) -> u32 {
+    let mut score = 0;
+    let mut state = Machine(Group, 0);
+    for c in input.chars() {
+        let next = state.next(c);
+        if next.1 > state.1 {
+            score += next.1;
+        }
+        state = next;
+    }
+    score
+}
+
+fn main() {
+    let mut input = String::new();
+    io::stdin().read_to_string(&mut input).unwrap();
+
+    println!("Part 1: {}", solve1(input.trim()));
+}
+
+#[test]
+fn part1() {
+    assert_eq!(1, solve1("{}"));
+    assert_eq!(6, solve1("{{{}}}"));
+    assert_eq!(5, solve1("{{},{}}"));
+    assert_eq!(16, solve1("{{{},{},{{}}}}"));
+    assert_eq!(1, solve1("{<a>,<a>,<a>,<a>}"));
+    assert_eq!(9, solve1("{{<ab>},{<ab>},{<ab>},{<ab>}}"));
+    assert_eq!(9, solve1("{{<!!>},{<!!>},{<!!>},{<!!>}}"));
+    assert_eq!(3, solve1("{{<a!>},{<a!>},{<a!>},{<ab>}}"));
+}