class FirstUniqueCharFinder {
 
  static String find(String word) {
    int len = word.length();
    String firstUniqueChar = null;
 
    for (int i = 0; i < len; i++) {
      String currentChar = word.substring(i, i + 1);
      String after = word.substring(i + 1, len);
      if (!after.contains(currentChar)) {
        firstUniqueChar = currentChar;
        break;
      }
    }
 
      return firstUniqueChar;
    }
 
  public static void main(String[] args) {
    System.out.println(find("transaction"));
    System.out.println(find("reverse"));
  }
}

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