Optimal Integer Alphabetic Trees in Linear Time

We show that optimal alphabetic binary trees can be constructed in O(n) time if the elements of the initial sequence are drawn from a domain that can be sorted in linear time. We describe a [6] hybrid algorithm that combines the bottom-up approach of the original Hu-Tucker algorithm with the top-down approach of Larmore and Przytycka’s Cartesian tree algorithms. The hybrid algorithm demonstrates the computational equivalence of sorting and level tree construction.