Second star.

src/bin/p03.rs

@@ -46,7 +46,7 @@ fn part1(lines: &[String]) {
             .expect("Expected at least one duplicate item");
 
         let priority = to_priority(outlier).unwrap();
-        println!("{} ({})", outlier, priority);
+        dbg!(outlier, priority);
         sum += priority;
 
         left_set.clear();
@@ -56,9 +56,35 @@ fn part1(lines: &[String]) {
     println!("Sum: {}", sum);
 }
 
-fn part2(_lines: &[String]) {}
+fn part2(lines: &[String]) {
+    const GROUP_SIZE: usize = 3;
+    let mut sets = Vec::with_capacity(GROUP_SIZE - 1);
+    for _ in 0..GROUP_SIZE - 1 {
+        sets.push(HashSet::<char>::new())
+    }
 
-#[cfg(test)]
-mod tests {
-    use super::*;
+    let mut sum: u32 = 0;
+    for chunk in lines.chunks(GROUP_SIZE) {
+        let mut outlier: Option<char> = None;
+        'outlier_search: for i in 0..GROUP_SIZE {
+            if i != GROUP_SIZE - 1 {
+                sets[i].clear();
+                chunk[i].chars().collect_into(&mut sets[i]);
+            } else {
+                for c in chunk[i].chars() {
+                    if sets[0..GROUP_SIZE - 1].into_iter().all(|s| s.contains(&c)) {
+                        outlier = Some(c);
+                        break 'outlier_search;
+                    }
+                }
+            }
+        }
+
+        let outlier = outlier.expect("Expect at least one outlier");
+        let priority = to_priority(outlier).unwrap();
+        dbg!(outlier, priority);
+        sum += priority;
+    }
+
+    println!("Sum: {}", sum);
 }