Detect Cycle in a Directed Graph

Detecting cycles in a directed graph is a common problem with wide-ranging applications in various domains such as network analysis, scheduling, and resource allocation. The algorithmic approach involves traversing the graph using depth-first search (DFS) and identifying back edges. If a back edge is encountered during the traversal, it indicates the presence of a cycle.

Algorithm Steps:

  • Initialize arrays for visited vertices and recursion stack.
  • Start DFS from each unvisited vertex.
  • Mark the current vertex as visited and add it to the recursion stack.
  • For each adjacent vertex:
    • If the vertex is not visited, recursively call DFS.
    • If the vertex is in the recursion stack, a cycle is detected.
  • Remove the current vertex from the recursion stack upon backtracking.

Applications:

  • Task scheduling in project management.
  • Resource allocation in computer systems.

Graph-Based Algorithms for GATE Exam [2024]

Ever wondered how computers figure out the best path in a maze or create efficient networks like a pro? That’s where Graph-Based Algorithms come into play! Think of them as your digital navigation toolkit. As you prepare for GATE 2024, let these algorithms be your allies, unraveling the intricacies of graphs and leading you to success.

Table of Content

  • Depth First Search or DFS for a Graph
  • Detect Cycle in a Directed Graph
  • Topological Sorting
  • Bellman–Ford Algorithm
  • Floyd Warshall Algorithm
  • Shortest path with exactly k edges in a directed and weighted graph
  • Biconnected graph
  • Articulation Points (or Cut Vertices) in a Graph
  • Check if a graph is strongly connected (Kosaraju’s Theorem)
  • Bridges in a graph
  • Transitive closure of a graph
  • Previously Asked GATE Questions on Graph-Based Algorithms

A Graph is a non-linear data structure consisting of vertices and edges. The vertices are sometimes also referred to as nodes and the edges are lines or arcs that connect any two nodes in the graph. More formally a Graph is composed of a set of vertices( V ) and a set of edges( E ). The graph is denoted by G(E, V).

In this comprehensive guide, we will explore key graph algorithms, providing detailed algorithm steps with its applications, which are relevance for the GATE Exam.

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1. Breadth First Search or BFS for a Graph (BFS):

BFS explores a graph level by level, visiting all neighbours of a node before moving on to the next level. It uses a queue data structure to maintain the order in which nodes are visited....

2. Depth First Search or DFS for a Graph:

DFS explores a graph by going as deep as possible along one branch before backtracking. It uses a stack (or recursion) to keep track of the visited nodes....

3. Detect Cycle in a Directed Graph:

Detecting cycles in a directed graph is a common problem with wide-ranging applications in various domains such as network analysis, scheduling, and resource allocation. The algorithmic approach involves traversing the graph using depth-first search (DFS) and identifying back edges. If a back edge is encountered during the traversal, it indicates the presence of a cycle....

4. Topological Sorting:

Topological sorting is vital for scheduling tasks with dependencies, and it is often used in project management and task scheduling. The algorithm involves linearly ordering the vertices of a directed acyclic graph (DAG) in such a way that for every directed edge ‘uv,’ vertex ‘u’ comes before ‘v’ in the ordering....

5. Bellman–Ford Algorithm:

The Bellman–Ford algorithm is employed for finding the shortest paths from a single source vertex to all other vertices in a weighted graph, even if the graph contains negative weight edges. This algorithm is particularly useful in scenarios where Dijkstra’s algorithm might fail due to negative weights....

6. Floyd Warshall Algorithm:

The Floyd Warshall algorithm is a dynamic programming approach to find the shortest paths between all pairs of vertices in a weighted graph. It works well for dense graphs and is capable of handling graphs with both positive and negative weights....

7. Shortest path with exactly k edges in a directed and weighted graph:

This problem involves finding the shortest path with a specific number of edges in a directed and weighted graph. The solution often relies on dynamic programming techniques to calculate the shortest paths for varying numbers of edges....

8. Biconnected graph:

A biconnected graph is a graph that remains connected even after the removal of any single vertex (and its incident edges). Biconnected graphs are crucial in designing robust network structures, and algorithms for identifying them are essential for network reliability....

9. Articulation Points (or Cut Vertices) in a Graph:

Articulation points are vertices whose removal would disconnect a graph. Detecting these points is essential in network design to ensure robustness and fault tolerance. Algorithms for finding articulation points often use depth-first search....

10. Check if a graph is strongly connected (Kosaraju’s Theorem):

Kosaraju’s Theorem provides an efficient algorithm for checking whether a directed graph is strongly connected, meaning there is a directed path from every vertex to every other vertex....

11. Bridges in a graph:

Bridges, also known as cut edges, are edges whose removal increases the number of connected components in a graph. Detecting bridges is crucial for network design and ensuring connectivity....

12. Transitive closure of a graph:

The transitive closure of a graph involves determining all pairs of vertices reachable from each other. Algorithms for transitive closure are vital in optimizing graph-related queries and analyses....

13. Minimum Spanning Tree (MST):

A minimum spanning tree (MST) of a connected undirected graph is a subgraph that includes the all the vertices of graph with the minimum possible total edge weight. The MSTs have the various applications in the network design, circuit wiring and clustering algorithms....

Previously Asked GATE Questions on Graph-Based Algorithms:

Question 1: Which of the following statements is/are TRUE for an undirected graph?P: Number of odd degree vertices is evenQ: Sum of degrees of all vertices is even...