Let G be a directed weighted graph with n vertices and m edges such that the edges in G have positive weights. Let (u, v) be an edge in G. By a shortest cycle containing edge (u, v) we mean a cycle containing (u, v) that is of minimum weight, among all cycles containing (u, v) (if such a cycle exists). Give an O(mlgn)-time algorithm that computes a shortest cycle in G containing the edge (u, or reports that no cycle containing edge (u, v) exists.
Let G be a directed weighted graph with n vertices and m edges such that the edges in G have positive weights. Let (u, v) be an edge in G. By a shortest cycle containing edge (u, v) we mean a cycle containing (u, v) that is of minimum weight, among all cycles containing (u, v) (if such a cycle exists). Give an O(mlgn)-time algorithm that computes a shortest cycle in G containing the edge (u, or reports that no cycle containing edge (u, v) exists.
Database System Concepts
7th Edition
ISBN:9780078022159
Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Chapter1: Introduction
Section: Chapter Questions
Problem 1PE
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Transcribed Image Text:**Title: Algorithm for Finding the Shortest Cycle in a Directed Weighted Graph Containing a Specific Edge**
**Introduction:**
Given a directed weighted graph \( G \) with \( n \) vertices and \( m \) edges, where all edges have positive weights, this page will guide you through deriving an algorithm to identify the shortest cycle containing a specific edge \( (u, v) \).
**Definition:**
- **Graph \( G \):** A structure consisting of vertices and edges.
- **Directed Graph:** Each edge has a direction, going from one vertex to another.
- **Weighted Graph:** Each edge has a weight (a positive number in this case).
- **Cycle:** A path starting and ending at the same vertex without traversing any vertex more than once except for the starting/ending vertex.
- **Shortest Cycle containing \( (u, v) \):** For a specified edge \( (u, v) \), it's the cycle that has the smallest total weight among all cycles that include the edge \( (u, v) \).
**Problem Statement:**
- **Objective:** To find the shortest cycle in \( G \) that includes the edge \( (u, v) \) or determine that no such cycle exists.
- **Constraint:** The algorithm must run in \( O(m \log n) \) time complexity.
**Algorithm Explanation:**
1. **Initialize Data Structures:**
- Use appropriate data structures to store the graph information, such as adjacency lists to represent the graph and a priority queue for the shortest path calculations.
2. **Weight Calculation:**
- Apply Dijkstra's algorithm or another shortest path algorithm that can handle positive weights efficiently to find the shortest path from \( v \) to \( u \) (excluding the edge \( (u, v) \)).
3. **Cycle Identification:**
- Calculate the total weight of the cycle by adding the weight of edge \( (u, v) \) to the shortest path found from \( v \) to \( u \).
- Check if a cycle exists by verifying if the shortest path from \( v \) to \( u \) is non-existent or has infinite weight (indicating no viable path).
4. **Output Result:**
- If a valid cycle is identified, report the cycle and its total weight.
- If no such cycle exists, report the absence of such a cycle.
**Mathematical Representation:**
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