code: static int[] insert(int[] itemset, int item) {
          if (itemset == null) {
              int[] newItemset = {item};
              return newItemset;
              
          } else {
              int n = itemset.length + 1;
              int[] newItemset = new int[n];
  
              newItemset[0] = item;
              System.arraycopy(itemset, 0, newItemset, 1, n - 1);
  
              return newItemset;
          }
      }
docs: Insert a item to the front of an item set.
  @param itemset the original item set.
  @param item the new item to be inserted.
  @return the combined item set