Day 9

1 files changed, 87 insertions, 0 deletions

diff --git a/src/bin/day09.rs b/src/bin/day09.rs
new file mode 100644
index 0000000..fb3046f
--- /dev/null
+++ b/src/bin/day09.rs
@@ -0,0 +1,87 @@
+use std::io::{self, Read};
+use std::str::FromStr;
+
+struct Chunk {
+    data: String,
+    repeat: u32,
+}
+
+impl Chunk {
+    fn len(&self) -> usize {
+        self.data.len() * self.repeat as usize
+    }
+
+    fn parse(s: &str) -> Result<(Self, &str), ()> {
+        if s.starts_with('(') {
+            let mut iter = s[1..].splitn(3, |ch| ch == 'x' || ch == ')');
+
+            let len = iter.next().ok_or(())?.parse().map_err(|_| ())?;
+            let repeat = iter.next().ok_or(())?.parse().map_err(|_| ())?;
+            let (data, rest) = iter.next().ok_or(())?.split_at(len);
+
+            let chunk = Chunk {
+                data: data.to_owned(),
+                repeat: repeat,
+            };
+
+            Ok((chunk, rest))
+        } else {
+            let paren = s.find('(').unwrap_or(s.len());
+
+            let chunk = Chunk {
+                data: s[..paren].to_owned(),
+                repeat: 1,
+            };
+            let rest = &s[paren..];
+
+            Ok((chunk, rest))
+        }
+    }
+}
+
+struct File {
+    chunks: Vec<Chunk>,
+}
+
+impl File {
+    fn len(&self) -> usize {
+        self.chunks.iter().map(Chunk::len).sum()
+    }
+}
+
+impl FromStr for File {
+    type Err = ();
+    fn from_str(mut s: &str) -> Result<Self, ()> {
+        let mut chunks = Vec::new();
+
+        while !s.is_empty() {
+            let (chunk, rest) = Chunk::parse(s)?;
+            chunks.push(chunk);
+            s = rest;
+        }
+
+        Ok(File { chunks: chunks })
+    }
+}
+
+fn solve(input: &str) -> usize {
+    let file: File = input.parse().unwrap();
+    file.len()
+}
+
+fn main() {
+    let mut input = String::new();
+    io::stdin().read_to_string(&mut input).unwrap();
+
+    println!("Part 1: {}", solve(&input));
+}
+
+#[test]
+fn part1() {
+    assert_eq!(6, solve("ADVENT"));
+    assert_eq!(7, solve("A(1x5)BC"));
+    assert_eq!(9, solve("(3x3)XYZ"));
+    assert_eq!(11, solve("A(2x2)BCD(2x2)EFG"));
+    assert_eq!(6, solve("(6x1)(1x3)A"));
+    assert_eq!(18, solve("X(8x2)(3x3)ABCY"));
+}