day05 part 2 prealloc vectors

src/tasks/day05.rs

@@ -36,7 +36,7 @@ pub fn task2() {
 fn reduce(input: &str) -> String {
     input
         .chars()
-        .fold(Vec::<char>::new(), |mut stack, c| {
+        .fold(Vec::<char>::with_capacity(input.len()), |mut stack, c| {
             let last: Option<char>;
             {
                 if let Some(c) = stack.last() {