code: public static int[] insertArray(int[] original, int index, int[] inserted) {
          int[] modified = new int[original.length + inserted.length];
          System.arraycopy(original, 0, modified, 0, index);
          System.arraycopy(inserted, 0, modified, index, inserted.length);
          System.arraycopy(original, index, modified, index + inserted.length, modified.length - index - inserted.length);
          return modified;
      }
docs: Inserts the specified array into the specified original array at the specified index.
  
  @param original the original array into which we want to insert another array
  @param index the index at which we want to insert the array
  @param inserted the array that we want to insert
  @return the combined array