 Since there is only one path from the root to any single node, each internal path represents a search for a specific element.If there are formula_2 elements, which is a positive integer, and the internal path length is formula_122, then the average number of iterations for a successful search formula_123, with the one iteration added to count the initial iteration.Since binary search is the optimal algorithm for searching with comparisons, this problem is reduced to calculating the minimum internal path length of all binary trees with formula_2 nodes, which is equal to