add day 13, part 2

day13/common.rs

@@ -16,7 +16,7 @@
 use std::cmp::{Ordering, PartialOrd};
 use std::io;
 
-#[derive(Debug, PartialEq, Clone)]
+#[derive(Debug, PartialEq, Clone, Eq, Ord)]
 pub enum Token {
     Integer(u64),
     List(Vec<Token>),

day13/part2.rs

@@ -0,0 +1,38 @@
+// Copyright 2022 Christian Ulrich
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+//
+// usage: ./part1 < input
+
+pub mod common;
+
+use common::Token;
+
+fn main() -> Result<(), &'static str> {
+    let mut packets = Vec::new();
+    for pair in common::packet_pairs() {
+        let (left, right) = pair?;
+        packets.push(left);
+        packets.push(right);
+    }
+    let divider1 = Token::from_str("[[2]]")?;
+    let divider2 = Token::from_str("[[6]]")?;
+    packets.push(divider1.clone());
+    packets.push(divider2.clone());
+    packets.sort();
+    let divider1_pos = packets.iter().position(|p| p == &divider1).unwrap() + 1;
+    let divider2_pos = packets.iter().position(|p| p == &divider2).unwrap() + 1;
+    println!("{}", divider1_pos * divider2_pos);
+    Ok(())
+}