// String reverse(String word) {
//   StringBuffer reversed = StringBuffer();
//   for (int i = 0; i < word.length; i++) {
//     reversed.write(word[word.length - 1 - i]);
//   }
//   return reversed.toString();
// }

String reverse(String word) {
  List<String> chars = word.split('');
  int left = 0;
  int right = chars.length - 1;
  while (left < right) {
    String temp = chars[left];
    chars[left] = chars[right];
    chars[right] = temp;
    left++;
    right--;
  }
  return chars.join('');
}