public boolean evaluate(String input) {
    validateInput(input);

    Set<Integer> charsCounter = new HashSet<Integer>();
    for (char c : input.toCharArray()) {
      if (charsCounter.contains((int) c)) {
        return false;
      } else {
        charsCounter.add((int) c);
      }
    }
    return true;
  }
Iterative algorithm to solve this problem. The complexity order of this algorithm in space an
time terms is equals to O(N) where N is the number of chars inside the input String passed as
parameter.
src/main/java/com/github/pedrovgs/problem50/UniqueChars.java