Detecting if a string has unique characters: comparing my solution to “Cracking the Coding Interview?”

Question

I am working through the book \"Cracking the Coding Interview\" and I have come across questions here asking for answers, but I need help comparing my answer to the solution

Answer 1

As referenced from 'Cracking the Coding Interview', an alternative solution exists:

boolean isUniqueChars(String str) {
  if(str.length() > 128) return false;

  boolean[] char_set = new boolean[128];
  for(int i = 0; i < str.length(); i++) {
    int val = str.charAt(i);

    if(char_set[val]) {
      return false;
    }
    char_set[val] = true;
  }
  return true;
}

Of course, to achieve better space complexity, please refer to the above example by @templatetypedef