day03: Make it solve part 2 instead

day03/src/main.rs

@@ -15,13 +15,19 @@ fn main() -> Result<(), Box<dyn error::Error>> {
 	let reader = BufReader::new(f);
 
 	let mut sum: u32 = 0;
+	let mut group_items: HashSet<u32> = HashSet::new();
 
-	for line in reader.lines() {
+	for (i, line) in reader.lines().enumerate() {
 		let line = line?;
-		let (c1, c2) = line.split_at(line.len() / 2);
-		let c1_set = set_from_str(c1);
-		let c2_set = set_from_str(c2);
-		sum += c1_set.intersection(&c2_set).sum::<u32>();
+		if group_items.is_empty() {
+			group_items = set_from_str(line.as_str());
+		} else {
+			group_items = set_from_str(line.as_str()).intersection(&group_items).cloned().collect();
+		}
+		if (i + 1) % 3 == 0 {
+			sum += group_items.iter().next().unwrap();
+			group_items.drain();
+		}
 	}
 
 	println!("{}", sum);