Priority Queues and Sorting for Read-Only Data

We revisit the random-access-machine model in which the input is given on a read-only random-access media, the output is to be produced to a write-only sequential-access media, and in addition there is a limited random-access workspace. The length of the input is N elements, the length of the output is limited by the computation itself, and the capacity of the workspace is O(S + w) bits, where S is a parameter specified by the user and w is the number of bits per machine word. We present a state-of-the-art priority queue—called an adjustable navigation pile—for this model. Under some reasonable assumptions, our priority queue supports minimum and insert in O(1) worst-case time and extract in O(N/S+lgS) worst-case time, where lgN ≤ S ≤ N/ lgN . We also show how to use this data structure to simplify the existing optimal O(N/S +N lgS)-time sorting algorithm for this model.