1 files changed, 129 insertions, 0 deletions
diff --git a/src/bin/2022/day13.rs b/src/bin/2022/day13.rs
new file mode 100644
index 0000000..d8d24d2
--- /dev/null
+++ b/src/bin/2022/day13.rs
@@ -0,0 +1,129 @@
+#![allow(dead_code)]
+#![allow(unused_variables)]
+
+use advent_of_code::prelude::*;
+
+#[derive(PartialEq, Eq, Clone, Debug)]
+pub enum Packet {
+    Int(usize),
+    List(Vec<Packet>),
+}
+
+impl PartialOrd for Packet {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+impl Ord for Packet {
+    fn cmp(&self, other: &Self) -> Ordering {
+        match self {
+            Self::Int(left) => match other {
+                Self::Int(right) => left.cmp(right),
+                Self::List(right) => {
+                    Self::List(vec![self.clone()]).cmp(other)
+                }
+            },
+            Self::List(left) => match other {
+                Self::Int(right) => {
+                    self.cmp(&Self::List(vec![other.clone()]))
+                }
+                Self::List(right) => left.cmp(right),
+            },
+        }
+    }
+}
+
+impl Packet {
+    fn parse(s: &str) -> Result<(Self, &str)> {
+        if let Some(mut s) = s.strip_prefix('[') {
+            let mut l = vec![];
+            while !s.starts_with([',', ']']) {
+                let (packet, next) = Self::parse(s)?;
+                l.push(packet);
+                match next.as_bytes()[0] {
+                    b',' => s = &next[1..],
+                    b']' => {
+                        s = next;
+                        break;
+                    }
+                    _ => bail!("failed to parse"),
+                }
+            }
+            Ok((Self::List(l), &s[1..]))
+        } else {
+            let end = s.find([',', ']']).unwrap_or(s.len());
+            Ok((Self::Int(s[..end].parse()?), &s[end..]))
+        }
+    }
+}
+
+impl std::str::FromStr for Packet {
+    type Err = anyhow::Error;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        let (packet, rest) = Packet::parse(s)?;
+        if !rest.is_empty() {
+            bail!("trailing data: '{}'", rest);
+        }
+        Ok(packet)
+    }
+}
+
+pub fn parse(fh: File) -> Result<Vec<(Packet, Packet)>> {
+    let mut lines = parse::raw_lines(fh);
+
+    let mut pairs = vec![];
+    loop {
+        let packet1 = lines.next().unwrap();
+        let packet2 = lines.next().unwrap();
+        pairs.push((packet1.parse()?, packet2.parse()?));
+        if let Some(line) = lines.next() {
+            assert_eq!(line, "");
+        } else {
+            break;
+        }
+    }
+    Ok(pairs)
+}
+
+pub fn part1(pairs: Vec<(Packet, Packet)>) -> Result<usize> {
+    let mut total = 0;
+    for (i, (left, right)) in pairs.iter().enumerate() {
+        if left <= right {
+            total += i + 1;
+        }
+    }
+    Ok(total)
+}
+
+pub fn part2(pairs: Vec<(Packet, Packet)>) -> Result<usize> {
+    let div_a = Packet::List(vec![Packet::List(vec![Packet::Int(2)])]);
+    let div_b = Packet::List(vec![Packet::List(vec![Packet::Int(6)])]);
+    let mut packets: Vec<Packet> = pairs
+        .into_iter()
+        .flat_map(|(left, right)| {
+            std::iter::once(left).chain(std::iter::once(right))
+        })
+        .chain(std::iter::once(div_a.clone()))
+        .chain(std::iter::once(div_b.clone()))
+        .collect();
+    packets.sort_unstable();
+    let idx_a =
+        packets.iter().position(|packet| packet == &div_a).unwrap() + 1;
+    let idx_b =
+        packets.iter().position(|packet| packet == &div_b).unwrap() + 1;
+    Ok(idx_a * idx_b)
+}
+
+#[test]
+fn test() {
+    assert_eq!(
+        part1(parse(parse::data(2022, 13).unwrap()).unwrap()).unwrap(),
+        6070
+    );
+    assert_eq!(
+        part2(parse(parse::data(2022, 13).unwrap()).unwrap()).unwrap(),
+        20758
+    );
+}