day15: functional hash implementation using fold()

15/src/main.rs

@@ -27,13 +27,12 @@ fn main() {
 // COMMON
 
 fn hash_string(s: &str) -> u64 {
-    let mut val = 0u64;
+    s.bytes().fold(0u64, |mut accum, val| {
-    for c in s.bytes() {
+        accum += val as u64;
-        val += c as u64;
+        accum *= 17;
-        val *= 17;
+        accum %= 256;
-        val %= 256;
+        accum
-    }
+    })
-    val
 }
 
 // PROBLEM 1 solution
@@ -81,7 +80,11 @@ impl LensBox {
     }
 
     fn total_lens_power(&self) -> u64 {
-        self.order.iter().enumerate().map(|(lens_idx, label)| (lens_idx+1) as u64 * self.lenses[label] as u64).sum()
+        self.order
+            .iter()
+            .enumerate()
+            .map(|(lens_idx, label)| (lens_idx + 1) as u64 * self.lenses[label] as u64)
+            .sum()
     }
 }
 
@@ -137,7 +140,11 @@ fn problem2<T: BufRead>(mut input: Lines<T>) -> u64 {
         inst.execute(&mut boxes);
     }
 
-    boxes.iter().enumerate().map(|(box_idx, b)| (box_idx + 1) as u64 * b.total_lens_power()).sum()
+    boxes
+        .iter()
+        .enumerate()
+        .map(|(box_idx, b)| (box_idx + 1) as u64 * b.total_lens_power())
+        .sum()
 }
 
 #[cfg(test)]