Update lib.rs

solutions/scytale_decoder/src/lib.rs

@@ -1,20 +1,11 @@
 pub fn scytale_decoder(s: String, letters_per_turn: u32) -> Option<String> {
-    if s.is_empty() || letters_per_turn == 0 {
-        None
-    } else {
-        let mut decoded_s = "".to_string();
-        let mut start = 0;
-
-        while decoded_s.len() < s.len() {
-            decoded_s.push(s.chars().nth(start).unwrap());
-
-            let mut next = start + letters_per_turn as usize;
-            while next < s.len() {
-                decoded_s.push(s.chars().nth(next).unwrap());
-                next += letters_per_turn as usize;
-            }
-            start += 1;
-        }
-        Some(decoded_s)
+    let k = letters_per_turn as usize;
+    if s.is_empty() || k == 0 {
+        return None;
     }
+    let mut res = vec![String::new(); k];
+    for (i, c) in s.chars().enumerate() {
+        res[i % k].push(c);
+    }
+    Some(res.concat())
 }