From 5eb58ad076f2cd435b11b140820da224b60b73d5 Mon Sep 17 00:00:00 2001
From: Aria <me@aria.rip>
Date: Mon, 2 Jan 2023 21:58:56 +0000
Subject: initial commit

---
 2022/src/day03.rs | 62 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 62 insertions(+)
 create mode 100644 2022/src/day03.rs

(limited to '2022/src/day03.rs')

diff --git a/2022/src/day03.rs b/2022/src/day03.rs
new file mode 100644
index 0000000..7e245de
--- /dev/null
+++ b/2022/src/day03.rs
@@ -0,0 +1,62 @@
+mod utils;
+
+use std::collections::HashSet;
+
+use utils::read_input;
+
+fn main() {
+    let input = read_input();
+
+    // Convert each line to a tuple of hashsets, one for each backpack pocket
+    let rucksack_items: Vec<_> = input
+        .lines()
+        .map(|line| (&line[..line.len() / 2], &line[line.len() / 2..]))
+        .map(|(a, b)| -> (HashSet<char>, HashSet<char>) {
+            (a.chars().collect(), b.chars().collect())
+        })
+        .collect();
+
+    let sum_error_priorities: u32 = rucksack_items
+        .iter()
+        .map(|(a, b)| {
+            *a.intersection(b)
+                .next()
+                .expect("no common item between two backpack segments!")
+        }) // Get common item
+        .map(priority)
+        .sum();
+
+    let sum_badge_priorities: u32 = rucksack_items // Construct chunked iterator
+        .iter()
+        .step_by(3)
+        .zip(rucksack_items.iter().skip(1).step_by(3))
+        .zip(rucksack_items.iter().skip(2).step_by(3))
+        .map(|(((e1l, e1r), (e2l, e2r)), (e3l, e3r))| {
+            for item in e1l.union(e1r) {
+                if (e2l.contains(item) || e2r.contains(item))
+                    && (e3l.contains(item) || e3r.contains(item))
+                {
+                    return *item;
+                }
+            }
+            panic!(
+                "group has no badge! {:?}",
+                ((e1l, e1r), (e2l, e2r), (e3l, e3r))
+            )
+        })
+        .map(priority)
+        .sum();
+
+    println!("Part 1: {}", sum_error_priorities);
+    println!("Part 2: {}", sum_badge_priorities);
+}
+
+fn priority(chr: char) -> u32 {
+    if chr.is_ascii_lowercase() {
+        chr as u32 - 96
+    } else if chr.is_ascii_uppercase() {
+        chr as u32 - 38
+    } else {
+        panic!("unrecognised item {}", chr)
+    }
+}
-- 
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