Refactor not to iterate over the temporary vector.

src/day4/mod.rs

@@ -49,17 +49,16 @@ pub fn two() -> Result<u32, AdventError> {
     let mut vec = Vec::<u32>::new();
     vec.resize(games.len(), 1);
     
-    for game in games.into_iter() {
+    Ok(games.into_iter().fold(0, | acc, game | {
         let my_winning_numbers = game.my_numbers.intersection(&game.winning_numbers);
         let nr_free_tickets = my_winning_numbers.count() as i32;
-        
+        let vec_index: usize = (game.id - 1) as usize;
         for index in game.id..(game.id + nr_free_tickets ) {
-            let nr_to_count = vec[(game.id - 1) as usize];
+            let nr_to_count = vec[vec_index];
             for _ in 0..nr_to_count {
                 vec[index as usize] += 1;
             }       
         }
-    }
-
-    Ok(vec.iter().sum())
+        acc + vec[vec_index]
+    }))
 }