The 7 Bridges of Königsberg Quiz
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Questions and Answers

What happens if adding an edge to a spanning tree generates a cycle?

  • The edge is temporarily included until all edges are considered.
  • The spanning tree is restructured to include the edge.
  • The edge is rejected and not included in the graph. (correct)
  • The edge is included in the graph.

In Kruskal's algorithm, what is the first step to be performed?

  • Identify all cycles in the current graph.
  • Start adding edges without sorting.
  • Sort the edges by increasing weight. (correct)
  • Select the edge with the maximum weight.

Why is cycle detection important in Kruskal's algorithm?

  • To ensure that all edges can connect any two vertices.
  • To verify that the spanning tree remains connected.
  • To prevent the inclusion of edges that would form a cycle. (correct)
  • To keep the total weight of the tree as low as possible.

When adding edges in Kruskal's algorithm, which edge is preferred first?

<p>The edge that has the least weightage. (B)</p> Signup and view all the answers

What is the significance of arranging edges in increasing order of weight?

<p>To ensure that the least costly options are considered first. (A)</p> Signup and view all the answers

What does the spanning tree property ensure?

<p>There are no cycles, and all vertices are connected. (C)</p> Signup and view all the answers

Which technique is primarily used in Kruskal's algorithm?

<p>Greedy approach. (B)</p> Signup and view all the answers

If an edge (E, G) is added and it creates a cycle, what should be done?

<p>Discard the edge to maintain the spanning tree property. (A)</p> Signup and view all the answers

What condition must be satisfied for a graph to have an Euler circuit?

<p>The graph must be connected and all vertices have even degrees. (C)</p> Signup and view all the answers

In the context of Eulerian paths, how many vertices can have an odd degree for such a path to exist?

<p>Exactly two odd degree vertices. (C)</p> Signup and view all the answers

What defines an odd vertex in graph theory?

<p>A vertex connected by an odd number of edges. (D)</p> Signup and view all the answers

Which of the following statements is true regarding Eulerian paths?

<p>An Eulerian path traverses every edge exactly once. (D)</p> Signup and view all the answers

What is a defining characteristic of an Euler circuit?

<p>It ends at the same vertex where it starts. (A)</p> Signup and view all the answers

When investigating the 7 Bridges of Königsberg problem, which conclusion did Euler reach?

<p>It is impossible to traverse all bridges exactly once. (C)</p> Signup and view all the answers

Which theorem states that a finite graph can have an Euler path if it is connected and exactly two vertices have odd degrees?

<p>Euler's Path Theorem. (B)</p> Signup and view all the answers

What is the implication of having all even degree vertices in a graph?

<p>The graph can have an Euler circuit. (B)</p> Signup and view all the answers

What property must a minimum spanning tree possess regarding the number of edges?

<p>It must have one less edge than the number of vertices. (B)</p> Signup and view all the answers

Which of the following statements best describes the greedy algorithm approach in finding a minimum spanning tree?

<p>It selects edges based on the smallest weight while avoiding cycles. (D)</p> Signup and view all the answers

When sorting edges by weight for the purpose of creating a minimum spanning tree, what is the primary goal?

<p>To minimize the total weight of the spanning tree. (C)</p> Signup and view all the answers

Which algorithm is commonly used for cycle detection in undirected graphs?

<p>Depth-First Search (DFS) (B)</p> Signup and view all the answers

In a graph, which of the following conditions would suggest the presence of a cycle?

<p>All vertices have an even degree. (A)</p> Signup and view all the answers

If a graph is acyclic and connected, what can be inferred about its structure?

<p>It is a spanning tree. (B)</p> Signup and view all the answers

What role does a queue play in the breadth-first search (BFS) algorithm?

<p>To manage the visited vertices during traversal. (B)</p> Signup and view all the answers

What is the primary concern when detecting cycles using the union-find method?

<p>Ensuring subsets of the graph remain disjoint. (D)</p> Signup and view all the answers

When creating a minimum spanning tree using Kruskal's algorithm, which step is taken after sorting all edges?

<p>Select the first edge and add it to the tree. (A)</p> Signup and view all the answers

What must be true of the edges selected in the process of forming a minimum spanning tree?

<p>They must not create any cycles. (D)</p> Signup and view all the answers

Study Notes

The 7 Bridges of Königsberg

  • Journey can start and finish at any point in the town.
  • The goal is to cross all seven bridges once and only once.
  • Represents a problem of drawing a network without lifting the pencil or retracing a line.
  • Euler defined odd and even vertices based on the number of arcs connected:
    • Odd vertex: odd number of arcs.
    • Even vertex: even number of arcs.
  • A graph has an Eulerian walk if it has either 0 or 2 odd degree vertices.

Euler Circuits and Paths

  • Euler Circuit: A circuit that visits every edge in a graph. Requires connected graph with all vertices of even degree.
  • Euler Path: A path that visits every edge; requires connected graph with exactly two odd degree vertices.

Graph Terminology

  • Graph G: An ordered pair of a set of vertices and a set of edges (2-subsets of vertices).
  • Simple Graph: No loops or multiple edges; consists only of distinct edges.
  • Directed Graph: Each edge has a direction, represented as ordered pairs (e.g., E = {(1,2), (3,2), (1,3)}).

Edge and Vertex Terminology

  • Endpoints: U and V are the endpoints of an edge.
  • Incident Edges: Edges connected to a specific vertex.
  • Degree of a Vertex: The count of edges emerging from it (e.g., a vertex X has degree 5).
  • Parallel Edges: Edges connecting the same pair of vertices.
  • Self-loop: An edge that connects a vertex to itself.
  • Adjacent Vertices/Edges: Vertices or edges sharing a common endpoint.

Path Definitions

  • Path: Sequence of alternating vertices and edges starting and ending with vertices.
  • Simple Path: A path where all vertices and edges are distinct.

Graph Properties

  • Property 1: Each edge is counted twice in terms of its incidence on vertices.
  • Property 2: Degree of any vertex is limited in undirected graphs without self-loops or multiple edges.

Graph Representation

  • Adjacency Matrix: Represents edges in a grid format with rows for vertices and columns for edges, using binary values (0 or 1).
  • Incidence Matrix: Shows the connection between vertices and edges where rows represent vertices and columns represent edges.

Graph Traversal - Breadth-First Search (BFS)

  • Gather vertices level by level using a queue to manage which vertex to explore next.
  • If a dead-end is reached, backtrack to explore other vertices.
  • Spanning tree properties must hold; if not, the edge is excluded.

Kruskal’s Algorithm

  • Step 1: Arrange all edges in increasing weight order.
  • Step 2: Select edges that do not cause a cycle when added to the graph.
  • Step 3: Start adding edges with the least weight to form a spanning tree, while ensuring no cycles are created.

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Description

Test your understanding of the famous problem of the 7 Bridges of Königsberg. In this quiz, you will explore routes within the town, attempting to cross all seven bridges exactly once. Can you find a valid path without retracing your steps?

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