From efe7c0f1e1c20cb69e52eb501b392ebf4526ec1e Mon Sep 17 00:00:00 2001
From: Sam Willcocks <sam@wlcx.cc>
Date: Thu, 15 Dec 2022 13:20:33 +0000
Subject: [PATCH] Add day3 part1

---
 src/bin/day3.rs | 38 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)
 create mode 100644 src/bin/day3.rs

diff --git a/src/bin/day3.rs b/src/bin/day3.rs
new file mode 100644
index 0000000..810c108
--- /dev/null
+++ b/src/bin/day3.rs
@@ -0,0 +1,38 @@
+/** Solution for Advent of Code 2022 day 3.
+ * https://adventofcode.com/2022/day/3
+ */
+use aoc2022::StdError;
+use std::collections::HashSet;
+use std::fs::File;
+use std::io::{BufRead, BufReader};
+
+fn main() -> StdError<()> {
+    // Open the input file and split all the lines.
+    let lines: Vec<_> = BufReader::new(File::open("input/day3.txt")?)
+        .lines()
+        .collect::<Result<_, _>>()?; // "Short circuit" any Errors in the iterator
+
+    let sum: u32 = lines
+        .iter()
+        .map(|l| {
+            assert!(l.len() % 2 == 0); // We won't be able to evenly split a odd-length line!
+            let (one, two) = (&l[0..l.len() / 2], &l[l.len() / 2..]);
+
+            // Make sets out of the characters in each compartment...
+            HashSet::<char>::from_iter(one.chars())
+                // ... then calculate the intersection, giving us the "items" (chars) in common
+                .intersection(&HashSet::from_iter(two.chars()))
+                .map(|c| match c {
+                    // Now, we map our "items" to their "priorities".
+                    // Fortunately we can cast all chars to u32, which makes this a matter of some
+                    // simple arithmetic.
+                    'a'..='z' => (*c as u32) - 'a' as u32 + 1,
+                    'A'..='Z' => (*c as u32) - 'A' as u32 + 27,
+                    _ => panic!("Got non-ascii alphabetic char!"),
+                })
+                .sum::<u32>() // Sum the priorities of items in common in each "rucksack"
+        })
+        .sum(); // Sum all the rucksacks' priorities
+    println!("Part 1: {}", sum);
+    Ok(())
+}