From 7e4c8522371f1bc8ed9c17581920557951c6cdf1 Mon Sep 17 00:00:00 2001
From: Jeremy Kaplan <jdkaplan@metagram.net>
Date: Fri, 2 Dec 2022 21:14:04 -0800
Subject: [PATCH] 2022 Day 3

---
 2022/Cargo.lock       | 16 +++++++++++++
 2022/Cargo.toml       |  1 +
 2022/src/bin/day03.rs | 52 +++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 69 insertions(+)
 create mode 100644 2022/src/bin/day03.rs

diff --git a/2022/Cargo.lock b/2022/Cargo.lock
index 91987e2..7d7bd32 100644
--- a/2022/Cargo.lock
+++ b/2022/Cargo.lock
@@ -13,4 +13,20 @@ name = "aoc2022"
 version = "0.1.0"
 dependencies = [
  "anyhow",
+ "itertools",
+]
+
+[[package]]
+name = "either"
+version = "1.8.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "90e5c1c8368803113bf0c9584fc495a58b86dc8a29edbf8fe877d21d9507e797"
+
+[[package]]
+name = "itertools"
+version = "0.10.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b0fd2260e829bddf4cb6ea802289de2f86d6a7a690192fbe91b3f46e0f2c8473"
+dependencies = [
+ "either",
 ]
diff --git a/2022/Cargo.toml b/2022/Cargo.toml
index 94bd1a2..0c7370c 100644
--- a/2022/Cargo.toml
+++ b/2022/Cargo.toml
@@ -5,3 +5,4 @@ edition = "2021"
 
 [dependencies]
 anyhow = "1.0.66"
+itertools = "0.10.5"
diff --git a/2022/src/bin/day03.rs b/2022/src/bin/day03.rs
new file mode 100644
index 0000000..ce7f24b
--- /dev/null
+++ b/2022/src/bin/day03.rs
@@ -0,0 +1,52 @@
+use std::collections::HashSet;
+
+use itertools::Itertools;
+
+const INPUT: &str = include_str!("../../input/day03.txt");
+
+fn main() {
+    println!("{}", part1(INPUT));
+    println!("{}", part2(INPUT));
+}
+
+fn part1(input: &str) -> usize {
+    let mut sum = 0;
+    for line in input.split('\n').filter(|l| !l.is_empty()) {
+        let mid = line.len() / 2;
+
+        let l = &line[..mid];
+        let r = &line[mid..];
+
+        let first: HashSet<char> = l.chars().collect();
+        let second: HashSet<char> = r.chars().collect();
+
+        let shared = first.intersection(&second).next().unwrap();
+        sum += priority(shared);
+    }
+    sum
+}
+
+const ALPHABET: &str = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
+
+fn priority(c: &char) -> usize {
+    1 + ALPHABET.chars().position(|x| x == *c).unwrap_or_default()
+}
+
+fn part2(input: &str) -> usize {
+    let mut sum = 0;
+    let lines = input.split('\n').filter(|l| !l.is_empty());
+    for group in &lines.chunks(3) {
+        let sets: Vec<HashSet<char>> = group
+            .map(|rucksack| rucksack.chars().collect::<HashSet<char>>())
+            .collect();
+
+        let mut shared = sets[0].clone();
+        shared = shared.intersection(&sets[1]).cloned().collect();
+        shared = shared.intersection(&sets[2]).cloned().collect();
+
+        let badge = shared.iter().next().unwrap();
+
+        sum += priority(badge);
+    }
+    sum
+}