Which of the following statement is false about Prim’s algorithm?

2020

Which of the following statement is false about Prim’s algorithm?

  1. A.

    Initially the root's key is initialized to 0 and all other nodes to infinity

  2. B.

    It may use binomial max heap to represent the priority queue

  3. C.

    The complexity is O(E log V) using binary heap

  4. D.

    The time complexity is O(E + V log V) using Fibonacci Heap

Attempted by 218 students.

Show answer & explanation

Correct answer: B

Concept: Prim's algorithm grows a Minimum Spanning Tree from a start vertex by repeatedly adding the cheapest edge that crosses from the tree to a vertex outside it (the cut property). To pick that cheapest crossing edge fast, every vertex keeps a key = the smallest edge weight connecting it to the current tree, and these keys are stored in a min-priority queue so that extract-min always returns the next vertex to attach.

Initialization: every vertex starts with key = infinity, then the start (root) vertex's key is set to 0 so it is the first one extracted. So the root's key is 0 while all other vertices begin at infinity and are lowered as cheaper edges are discovered.

Application — checking each statement against this method:

  • "binomial max heap for the priority queue" — Prim's needs the MINIMUM-weight vertex each step, which a min-priority queue (min-heap) provides. A max-heap returns the largest key, so it cannot drive Prim's; this claim does not hold.

  • "root key initialized to 0" — consistent with the initialization above: the start vertex's key is set to 0 (others are infinity), so this holds.

  • "O(E log V) using a binary heap" — with a binary heap each of the O(E) decrease-key and O(V) extract-min operations costs O(log V), giving O(E log V); this holds.

  • "O(E + V log V) using a Fibonacci heap" — a Fibonacci heap does decrease-key in O(1) amortized and extract-min in O(log V) amortized, giving O(E + V log V); this holds.

Cross-check: three statements match standard Prim's behaviour, so the single statement that is false about Prim's algorithm is the one claiming a binomial max heap can represent the priority queue.

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