Problem1-1.java

public boolean checkUniqueness(String source) {
  // Assumes that string includes ASCII characters (0-256)
  if (source == null || source.length() == 0 || source.length() > 256) { 
    return false;
  }
  
  boolean[] seen = new boolean[256];
  
  for (int i = 0; i < source.length(); i++) {
    int temp = (int) source.charAt(i);
    if (seen[temp]) {
      return false;
    }
    
    seen[temp] = true;
  }
  
  return true;
}