diff --git a/cli/src/main.rs b/cli/src/main.rs
index 55d9ed4..c8df5e9 100644
--- a/cli/src/main.rs
+++ b/cli/src/main.rs
@@ -152,7 +152,11 @@ async fn main() {
             }
             timings.drain(..=(warmup as usize));
             let avg = (timings.iter().sum::<Duration>() / n).as_nanos();
-            let deviation = (((timings.iter().max().unwrap().as_nanos() - timings.iter().min().unwrap().as_nanos()).pow(2) / 16) as f64).sqrt() as u128;
+            let deviation = (((timings.iter().max().unwrap().as_nanos()
+                - timings.iter().min().unwrap().as_nanos())
+            .pow(2)
+                / 16) as f64)
+                .sqrt() as u128;
 
             let (avg, avg_units) = if avg >= 1000000000 {
                 (avg as f64 / 1000000000.0, "s")
diff --git a/lib/src/day15/mod.rs b/lib/src/day15/mod.rs
index 9c50551..6da0bf0 100644
--- a/lib/src/day15/mod.rs
+++ b/lib/src/day15/mod.rs
@@ -1,5 +1,3 @@
-use std::collections::HashMap;
-
 use crate::utils::Day;
 
 #[derive(Debug, Default)]
@@ -9,65 +7,61 @@ pub struct Day15 {
 
 impl Day for Day15 {
     fn part1(&mut self) -> String {
-        let mut current = 0usize;
-
         self.input
             .split(',')
             .map(|text| {
-                current = 0;
-
-                for c in text.chars() {
-                    current += c as usize;
-                    current *= 17;
-                    current %= 256;
-                }
-
-                current
+                text.chars()
+                    .fold(0usize, |acc, c| ((acc + c as usize) * 17) % 256)
             })
             .sum::<usize>()
             .to_string()
     }
 
     fn part2(&mut self) -> String {
-        let mut map =
-            HashMap::<usize, Vec<(&str, u8)>>::from_iter((0..=255usize).map(|i| (i, vec![])));
+        const ARRAY_REPEAT_VALUE: Vec<(&str, u8)> = Vec::new();
+        let mut boxes: [Vec<(&str, u8)>; 256] = [ARRAY_REPEAT_VALUE; 256];
 
         for operation in self.input.split(',') {
-            let (label, focal_length) = operation.split_once(['-', '=']).unwrap();
-            let box_id = {
-                let mut current = 0;
+            let ((box_id, label), focal_length) = operation
+                .split_once(['-', '='])
+                .map(|(label, focal_length)| {
+                    (
+                        (
+                            label
+                                .chars()
+                                .fold(0usize, |acc, c| ((acc + c as usize) * 17) % 256),
+                            label,
+                        ),
+                        focal_length.parse::<u8>().ok(),
+                    )
+                })
+                .unwrap();
 
-                for c in label.chars() {
-                    current += c as usize;
-                    current *= 17;
-                    current %= 256;
+            match focal_length {
+                Some(focal_length) => {
+                    let lenses = boxes.get_mut(box_id).unwrap();
+                    match lenses.iter().position(|(l, _)| l == &label) {
+                        Some(position) => lenses[position].1 = focal_length,
+                        None => lenses.push((label, focal_length)),
+                    }
                 }
-
-                current
-            };
-            if focal_length == "" {
-                let lenses = map.get_mut(&box_id).unwrap();
-                if let Some(position) = lenses.iter().position(|(l, _)| l == &label) {
-                    lenses.remove(position);
-                }
-            } else {
-                let focal_length = focal_length.parse::<u8>().unwrap();
-
-                let lenses = map.get_mut(&box_id).unwrap();
-                match lenses.iter().position(|(l, _)| l == &label) {
-                    Some(position) => lenses[position].1 = focal_length,
-                    None => lenses.push((label, focal_length)),
+                None => {
+                    let lenses = boxes.get_mut(box_id).unwrap();
+                    if let Some(position) = lenses.iter().position(|(l, _)| l == &label) {
+                        lenses.remove(position);
+                    }
                 }
             }
         }
 
         (0..=255usize)
             .map(|i| {
-                map.remove(&i)
+                boxes
+                    .get(i)
                     .unwrap()
                     .into_iter()
                     .enumerate()
-                    .map(|(j, (_, focal_length))| focal_length as usize * (j + 1) * (i + 1))
+                    .map(|(j, (_, focal_length))| *focal_length as usize * (j + 1) * (i + 1))
                     .sum::<usize>()
             })
             .sum::<usize>()
diff --git a/rust-toolchain.toml b/rust-toolchain.toml
new file mode 100644
index 0000000..5d56faf
--- /dev/null
+++ b/rust-toolchain.toml
@@ -0,0 +1,2 @@
+[toolchain]
+channel = "nightly"