day(03): make helper functions

Signed-off-by: Matej Focko <mfocko@redhat.com>

src/bin/day03.rs

@@ -37,29 +37,38 @@ impl FromStr for Backpack {
     }
 }
 
+impl Backpack {
+    fn common_items(&self) -> HashSet<i32> {
+        let Backpack(left, right) = self;
+        left.intersection(right).cloned().collect()
+    }
+
+    fn all_items(&self) -> HashSet<i32> {
+        let Backpack(left, right) = self;
+        left.union(right).cloned().collect()
+    }
+}
+
 fn part_1(input: &Input) -> Output {
     input
         .iter()
-        .map(|Backpack(left, right)| left.intersection(right).sum::<i32>())
+        .map(|b| b.common_items().iter().sum::<i32>())
         .sum()
 }
 
+fn common_items(backpacks: &[Backpack]) -> HashSet<i32> {
+    backpacks
+        .iter()
+        .skip(1)
+        .fold(backpacks[0].all_items(), |u, b| {
+            u.intersection(&b.all_items()).cloned().collect()
+        })
+}
+
 fn part_2(input: &Input) -> Output {
     input
-        .iter()
-        .map(|Backpack(left, right)| left.union(right).cloned().collect())
-        .collect::<Vec<HashSet<i32>>>()
         .chunks(3)
-        .map(|sets| {
+        .map(|backpacks| common_items(backpacks).iter().sum::<i32>())
-            // debug!("Sets: {:?}", sets);
-            sets.iter()
-                .skip(1)
-                .fold(sets[0].clone(), |acc, s| {
-                    acc.intersection(s).cloned().collect()
-                })
-                .iter()
-                .fold(0, |acc, x| acc + *x)
-        })
         .sum()
 }