private void cleanUpHistory(){
  if (!mHistoryOfNumbers.isEmpty() && mHistoryOfNumbers.size() >= MAX_HISTORY_SIZE) {
    for (int i=0; i < Math.max(1,MAX_HISTORY_SIZE / 2); i++) {
      mPreviousNumbers.remove(mHistoryOfNumbers.removeFirst());
    }
  }
}

private void cleanUpHistory ( ) { if ( ! mHistoryOfNumbers . isEmpty ( ) && mHistoryOfNumbers . size ( ) >= MAX_HISTORY_SIZE ) { for ( int i = 0 ; i < Math . max ( 1 , MAX_HISTORY_SIZE / 2 ) ; i ++ ) { mPreviousNumbers . remove ( mHistoryOfNumbers . removeFirst ( ) ) ; } } }
removes old tracks and cleans up the history preparing for new tracks to be added to the mapping
