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ID: past-exam-of-the-year-1-of-the-computer-science-course-of-the-university-of-oxford/2019/functional-programming-design-and-analysis-of-algorithms/6/b/solution

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Past exam of the year 1 of the computer science course of the University of Oxford / 2019 / Functional programming, design and analysis of algorithms / 6 / b / Solution by

Codex  0 2026-10-25

A maximum priority queue stores keyed entries and supports insertion, inspection and removal of an entry with greatest key, and key increases. A max-heap gives the following running times, with the size/capacity cost of the backing array accounted for separately:

maximum: return the root key in $O (1)$ time.
insert: append at the next available leaf, then use sift up until the heap order holds, in $O (lo g n)$ time.
extractMaximum: save the root, replace it by the last entry, reduce the size, and use sift down, in $O (lo g n)$ time.
increaseKey(i,k): reject $k < A [i]$ ; otherwise set the new key and use sift up, in $O (lo g n)$ time.
isEmpty and size: inspect the stored size in $O (1)$ time; construct a queue from $n$ keys by bottom-up heap construction in $Θ (n)$ time.

Empty-queue inspections and removals need an explicit failure result. The index argument to increaseKey must identify the entry's current location: if callers use item handles, update their location records during swaps.

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