Lec 78 - Minimum Cost Spanning Trees: Kruskal's Algorithm

IIT Madras - B.S. Degree Programme12 minutes read

Kruskal's Algorithm and Prim's Algorithm both find minimum cost spanning trees in weighted undirected graphs but follow different strategies and sequences. Kruskal's Algorithm connects components with the smallest edge, avoiding cycles and sorting edges by weight, while Prim's Algorithm grows the tree gradually, leading to multiple possible spanning trees with repeated edge weights.

Insights

  • Kruskal's Algorithm and Prim's Algorithm both find the same minimum cost spanning tree but follow distinct processes, with Kruskal's focusing on sorting edges and connecting components without cycles, while Prim's grows the tree incrementally.
  • In scenarios where edge weights are repeated, multiple spanning trees with the same minimum cost could emerge due to different edge sets resulting from varying vertex ordering, showcasing the impact of seemingly minor details on the final outcome.

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Recent questions

  • What are the two main strategies for minimum cost spanning trees?

    Prim's strategy and Kruskal's Algorithm

  • How does Kruskal's Algorithm avoid creating cycles?

    By skipping edges that connect vertices within the same component.

  • What is the key principle behind Kruskal's Algorithm?

    Adding the smallest edge connecting different components.

  • How does Kruskal's Algorithm differ from Prim's Algorithm in tree construction?

    Kruskal's Algorithm assembles the tree bottom-up, while Prim's Algorithm grows the tree gradually.

  • How do repeated edge weights impact the construction of spanning trees?

    They may lead to multiple possible spanning trees with different edge sets.

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Summary

00:00

Comparing Kruskal's and Prim's Minimum Spanning Trees

  • Minimum cost spanning trees are discussed, with two main strategies: Prim's strategy and Kruskal's Algorithm.
  • Weighted undirected graphs are used, with a weight function for each edge, assuming graph connectivity.
  • Kruskal's Algorithm starts with disconnected vertices forming components, merging them with the smallest connecting edge.
  • Example of Kruskal's Algorithm implementation involves sorting edges in ascending order and connecting components.
  • The algorithm avoids creating cycles by skipping edges that connect vertices within the same component.
  • Kruskal's Algorithm and Prim's Algorithm find the same minimum cost spanning tree but in different sequences.
  • Kruskal's Algorithm involves sorting edges by weight, tracking added edges, and connecting components without cycles.
  • The algorithm ensures the smallest edge connecting different components is added, following the minimum separator lemma.
  • Kruskal's Algorithm assembles the tree bottom-up, while Prim's Algorithm grows the tree gradually.
  • Repeated edge weights may lead to multiple possible spanning trees, with different choices affecting the outcome.

12:19

Different spanning trees with same cost.

  • Edge weights repeating can lead to different spanning trees with the same minimum cost but different edge sets, based on vertex ordering.
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