Add (still messy) part 2 solution for day 18

day18/Cargo.lock

@@ -12,10 +12,17 @@ checksum = "cdb031dd78e28731d87d56cc8ffef4a8f36ca26c38fe2de700543e627f8a464a"
 name = "day18"
 version = "0.1.0"
 dependencies = [
+ "itertools",
  "nom",
  "petgraph",
 ]
 
+[[package]]
+name = "either"
+version = "1.6.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e78d4f1cc4ae33bbfc157ed5d5a5ef3bc29227303d595861deb238fcec4e9457"
+
 [[package]]
 name = "fixedbitset"
 version = "0.4.0"
@@ -38,6 +45,15 @@ dependencies = [
  "hashbrown",
 ]
 
+[[package]]
+name = "itertools"
+version = "0.10.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a9a9d19fa1e79b6215ff29b9d6880b706147f16e9b1dbb1e4e5947b5b02bc5e3"
+dependencies = [
+ "either",
+]
+
 [[package]]
 name = "memchr"
 version = "2.4.1"

day18/Cargo.toml

@@ -8,3 +8,4 @@ edition = "2021"
 [dependencies]
 nom = "7.1"
 petgraph = "0.6"
+itertools = "0.10"

day18/src/main.rs

@@ -1,5 +1,5 @@
 #![warn(clippy::all, clippy::pedantic)]
-use std::collections::HashSet;
+use itertools::Itertools;
 use std::env;
 use std::fmt;
 use std::fmt::Debug;
@@ -494,6 +494,29 @@ fn part1(input_pairs: &[InputPair]) -> u32 {
     problem_tree.magnitude()
 }
 
+fn part2(input_pairs: &[InputPair]) -> u32 {
+    input_pairs
+        .into_iter()
+        .permutations(2)
+        .map(|pairs| {
+            let pair1 = pairs[0];
+            let pair2 = pairs[1];
+
+            let mut tree1 = if let InputPair::Pair(left, right) = pair1 {
+                ProblemTree::build(&*left, &*right)
+            } else {
+                panic!("input pair should be a pair");
+            };
+
+            tree1.insert_root_sibling_input_pair(pair2, Direction::Right);
+            tree1.reduce();
+
+            tree1.magnitude()
+        })
+        .max()
+        .expect("should be at least one input pair")
+}
+
 fn print_tree(problem_tree: &ProblemTree) {
     println!("{:?}", Dot::with_config(&problem_tree.graph, &[]));
     // let mut to_visit = vec![(0, problem_tree.root_idx)];
@@ -538,4 +561,5 @@ fn main() {
     // .expect("did not find input problem");
 
     println!("Part 1: {}", part1(&all_pairs));
+    println!("Part 2: {}", part2(&all_pairs));
 }