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GATE CSE 2020 Q59: MST weight of a complete graph with weights |i − j|

Question

Consider a graph G=(V,E)G = (V, E), where V={v1,v2,…,v100}V = \{v_1, v_2, \ldots, v_{100}\}, E={(vi,vj)∣1≤i<j≤100}E = \{(v_i, v_j) \mid 1 \le i < j \le 100\}, and weight of the edge (vi,vj)(v_i, v_j) is ∣i−j∣|i - j|. The weight of minimum spanning tree of GG is _______.

Try it: numerical answer: type the value

Numerical answer. No negative marking.
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Answer: 99 (official GATE 2020 final answer key)

Concept used: Every edge has weight at least 1, and a spanning tree on 100 vertices has 99 edges.

First step: The path v1−v2−⋯−v100v_1 - v_2 - \cdots - v_{100} uses only weight-1 edges and spans all vertices.

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Source: official GATE 2020 CS question paper and final answer key, organised by IIT Delhi. Question paper · Answer key