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Official PYQ · 2019

GATE CS 2019 Q38 — Graphs: Connectivity, Matching, Colouring

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Let GG be any connected, weighted, undirected graph.

  1. GG has a unique minimum spanning tree, if no two edges of GG have the same weight.
  2. GG has a unique minimum spanning tree, if, for every cut of GG, there is a unique minimum-weight edge crossing the cut.

Which of the following statements is/are TRUE?

Choose one option
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Answer: C

Statement I is TRUE: If all edge weights in a connected, undirected graph GG are distinct, then GG has a unique minimum spanning tree (MST). This is a fundamental property of MSTs, which can be proved using the cycle property (the heaviest edge on any cycle cannot belong to any MST).

Statement II is TRUE: The Cut Property states that for any cut of a graph, the minimum-weight edge crossing the cut must belong to every MST. If for every cut there is a unique minimum-weight edge crossing it, then that specific edge must be included in every MST of GG. Since the choice of the minimum-weight edge for every cut is unique, there is no ambiguity or alternative choice at any step of constructing the MST (e.g., in Prim's or Kruskal's algorithm), which guarantees a unique MST.

Thus, both statements I and II are TRUE.

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