public PhoneDirectory(int maxNumbers){
  set=new LinkedHashSet<>();
  for (int i=0; i < maxNumbers; i++) {
    set.add(i);
  }
}

public PhoneDirectory ( int maxNumbers ) { set = new LinkedHashSet < > ( ) ; for ( int i = 0 ; i < maxNumbers ; i ++ ) { set . add ( i ) ; } }
initialize your data structure here
