docs: public static IntMultimap invertFrom(Multimap<? extends Integer, ? extends Integer> map) {
      if (map instanceof IntMultimap) {
        IntMultimap other = (IntMultimap) map;
        // This is unnecessary, but it makes this method easier to implement.
        other.reindexItems();
  
        int[] newSortedKeys = Arrays.copyOf(other.sortedValues, other.sortedValues.length);
        int[] newSortedValues = Arrays.copyOf(other.sortedKeys, other.sortedKeys.length);
       
        ArrayUtils.sortKeyValuePairs(newSortedKeys, newSortedValues, 0, newSortedKeys.length);
  
        return new IntMultimap(newSortedKeys, newSortedValues);
      } else {
        IntMultimap inverse = IntMultimap.create();
        Multimaps.invertFrom(map, inverse);
        return inverse;
      }
    }