In the Apriori algorithm, we can use a hash tree data structure to efficiently count the support of candidate itemsets. Consider the hash tree for candidate 3-itemsets shown in Figure 6.32.
(a) Based on this figure, how many candidate 3-itemsets are there in total?
(b) Given a transaction that contains items {1, 2, 5, 6, 8}, which of the hash tree leaf nodes will be visited when finding the candidate 3-itemsets contained in the transaction?