iterative reverse string solution in dart

Author: nkawaller

Diff for: dart/0344-reverse-string.dart

@@ -0,0 +1,15 @@
+// Time Complexity: O(n)
+// Space Complexity: O(1)
+
+class Solution {
+  void reverseString(List<String> s) {
+    var l = 0, r = s.length - 1;
+    while (l <= r) {
+      var tmp = s[l]; 
+      s[l] = s[r]; 
+      s[r] = tmp;
+      l += 1; 
+      r -= 1;
+    }
+  }
+}