test

public static boolean isUniqueChars2(String str) {
  if (str.length() > 256) {
   return false;
  }
  boolean[] char_set = new boolean[256];
  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;
 }