Day 3, puzzle 2

src/bin/d3p1.rs

@@ -0,0 +1,15 @@
+use aoc22::day3;
+use aoc22::util;
+
+pub fn main() {
+    let rucksacks = day3::parse_rucksacks(&util::parse_input());
+
+    let mut sum = 0;
+    for (first, second) in rucksacks {
+        let common: Vec<_> = first.intersection(&second).collect();
+        assert!(common.len() == 1);
+        sum += day3::priority(**common.first().unwrap());
+    }
+
+    println!("Sum of priorities is {}", sum);
+}

src/bin/d3p2.rs

@@ -0,0 +1,17 @@
+use aoc22::day3;
+use aoc22::util;
+
+pub fn main() {
+    let rucksacks = day3::parse_rucksacks(&util::parse_input());
+
+    let mut sum = 0;
+    for group in rucksacks.chunks_exact(3) {
+        // Intersection of the unions of each rucksack's compartments
+        let common = &(&(&group[0].0 | &group[0].1) & &(&group[1].0 | &group[1].1))
+            & &(&group[2].0 | &group[2].1);
+        assert!(common.len() == 1);
+        sum += day3::priority(*common.iter().next().unwrap());
+    }
+
+    println!("Sum of priorities is {}", sum);
+}

src/day3.rs

@@ -0,0 +1,25 @@
+use std::collections::HashSet;
+
+pub fn parse_rucksacks(input: &String) -> Vec<(HashSet<char>, HashSet<char>)> {
+    let lines = input.lines();
+    let mut rucksacks = Vec::new();
+
+    for line in lines {
+        let length = line.len();
+        assert!(length % 2 == 0);
+        let (first, second) = line.split_at(length / 2);
+        rucksacks.push((first.chars().collect(), second.chars().collect()));
+    }
+
+    rucksacks
+}
+
+pub fn priority(c: char) -> u32 {
+    assert!(c.is_ascii_alphabetic());
+    let ord = c as u32;
+    if c.is_ascii_lowercase() {
+        1 + ord - 'a' as u32
+    } else {
+        27 + ord - 'A' as u32
+    }
+}

src/lib.rs

@@ -1,3 +1,4 @@
 pub mod day1;
 pub mod day2;
+pub mod day3;
 pub mod util;