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Module 3: Graph and Tree Algorithms

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If all edge weights in a graph are positive, what is the minimum number of edges in a spanning tree for a graph with vertices?

(i) V
(ii) V-1
(iii) V+1
(iv) 2V

Worked SolutionAI Assisted

Answer: (ii) V−1V-1

Explanation:

  • A spanning tree of a connected graph with VV vertices is a tree that includes all VV vertices.
  • Any tree with VV vertices has exactly V−1V-1 edges (proof by induction; also ∣E∣=∣V∣−1|E|=|V|-1 characterizes trees among connected graphs).
  • Edge weights (positive or otherwise) do not affect the count — any spanning tree, regardless of weight, has V−1V-1 edges. Minimum spanning tree also has V−1V-1 edges; weight affects which edges, not how many.
  • Additional edges would create a cycle → not a tree.

Correct choice: (ii) V−1V-1 (if graph disconnected, spanning forest has V−cV-c edges for cc components).

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