day3. Actually had some errors from the borrow checker! Luckily I could

just do what it told me to do, instead of having to actually
_understand_ anything about it... for now.

day3/src/main.rs

@@ -0,0 +1,37 @@
+fn main() {
+    let contents = std::fs::read_to_string("data.txt").expect("Failed to read file");
+    let lines: Vec<&str> = contents.lines().collect();
+
+    // Part 1
+    let sacks: Vec<(&str, &str)> = lines.iter().map(|&x| x.split_at(x.len() / 2)).collect();
+    let common_items_part1: Vec<char> = sacks.iter().map(find_common_item).collect();
+    let priorities_part1: Vec<u32> = common_items_part1.iter().map(char_to_code).collect();
+    let sum_part1: u32 = priorities_part1.iter().sum();
+    println!("Part 1 Sum: {sum_part1}");
+
+    // Part 2
+    let groups: Vec<&[&str]> = lines.chunks(3).collect();
+    let common_items_part2: Vec<char> = groups.iter().map(find_badge).collect();
+    let priorities_part2: Vec<u32> = common_items_part2.iter().map(char_to_code).collect();
+    let sum_part2: u32 = priorities_part2.iter().sum();
+    println!("Part 2 Sum: {sum_part2}");
+}
+
+fn char_to_code(c: &char) -> u32 {
+    let offset = if c.is_ascii_uppercase() { 38 } else { 96 };
+    *c as u32 - offset
+}
+
+fn find_common_item(pair: &(&str, &str)) -> char {
+    pair.0
+        .chars()
+        .filter(|&x| pair.1.contains(x))
+        .collect::<Vec<char>>()[0]
+}
+
+fn find_badge(set: &&[&str]) -> char {
+    set[0]
+        .chars()
+        .filter(|&x| set[1].contains(x) && set[2].contains(x))
+        .collect::<Vec<char>>()[0]
+}