day01-2 use scan with tuple expansion

The previous problem with this was, that I tried returning
"Some((Ref<i32>, _))" from the lambda. That caused the compiler to complain
about the lifetime of the `current` value, since I tried passing on the Ref
instead of the encapsulated value.

src/tasks/day01.rs

@@ -7,29 +7,23 @@ pub fn task1() {
         .map(|line| line.parse::<i32>().unwrap())
         .sum();
 
-    println!("Result: {}", frequency);
+    println!("Part 1: {}", frequency);
 }
 
 pub fn task2() {
-    let contents = utils::read_file("input/day01.txt");
+    let start_state = (vec![0].into_iter().collect::<HashSet<i32>>(), 0);
-
+    let final_state = utils::read_file("input/day01.txt")
-    let mut seen: HashSet<i32> = HashSet::new();
-    seen.insert(0);
-    let start_state = (std::cell::RefCell::new(seen), std::cell::RefCell::new(0));
-    let final_state = contents
         .lines()
         .map(|line| line.parse::<i32>().unwrap())
         .cycle()
-        .scan(&start_state, |(hash_set, current_freq), freq_change| {
+        .scan(start_state, |(set, current), freq_change| {
-            *current_freq.borrow_mut() += freq_change;
+            *current += freq_change;
-            if hash_set.borrow_mut().contains(&current_freq.borrow()) {
+            if set.insert(*current) {
-                Some((current_freq.borrow(), true))
+                Some((*current, false))
             } else {
-                let value: i32 = *current_freq.borrow_mut();
+                Some((*current, true))
-                hash_set.borrow_mut().insert(value);
-                Some((current_freq.borrow(), false))
             }
         }).find(|state| state.1);
 
-    println!("{:?} was there already!", final_state.unwrap().0);
+    println!("Part 2: {} was there already!", final_state.unwrap().0);
 }