C++ Boost Graph

Creating a C++ Boost Undirected Graph and Traversing It in Depth First Search Order

Graph theory is a key area of computer science and programming, and one of the most commonly used libraries for implementing graph algorithms in C++ is Boost. In this blog post, we’ll tackle the challenge of creating an undirected graph using the Boost library and then traverse it using the Depth First Search (DFS) method.

Introduction to the Problem

Creating and working with graphs can be daunting, but with Boost, it becomes much simpler. Depth First Search (DFS) is a fundamental algorithm used to explore vertices and edges of a graph. Whether you’re looking for pathways, checking connectivity, or solving puzzles, DFS is an efficient way to navigate through graphs.

In this post, we’ll explore a concrete example of setting up an undirected graph and implementing DFS traversal.

Solution Overview

We will cover the following steps:

  1. Include the necessary Boost headers.
  2. Define the graph structure.
  3. Create a visitor class for handling vertex discovery.
  4. Set up the main function to build the graph and perform DFS.

Step 1: Include Necessary Boost Headers

First and foremost, you need to include the Boost Graph headers, which provide the fundamental classes and functions for graph-related operations.

#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/depth_first_search.hpp>
#include <iostream>

Step 2: Define the Graph Structure

We define our undirected graph using the boost::adjacency_list. Here’s how you can define it:

typedef boost::adjacency_list<boost::listS, boost::vecS, boost::undirectedS> MyGraph;
typedef boost::graph_traits<MyGraph>::vertex_descriptor MyVertex;
  • In the code above:
    • listS indicates that the graph will use a list of edges.
    • vecS means we will use a vector to store vertices.
    • undirectedS specifies that the graph is undirected.

Step 3: Create a Visitor Class

The visitor class is crucial for defining what happens when a vertex is discovered during DFS. Here’s an example of a simple visitor class:

class MyVisitor : public boost::default_dfs_visitor {
public:
  void discover_vertex(MyVertex v, const MyGraph& g) const {
    std::cerr << v << std::endl; // Print the vertex number
    return;
  }
};

Step 4: Set Up the Main Function

Finally, we need to create the graph, add edges, and invoke the DFS algorithm.

int main() {
  MyGraph g;
  boost::add_edge(0, 1, g); // Connect vertex 0 and 1
  boost::add_edge(0, 2, g); // Connect vertex 0 and 2
  boost::add_edge(1, 2, g); // Connect vertex 1 and 2
  boost::add_edge(1, 3, g); // Connect vertex 1 and 3

  MyVisitor vis;
  boost::depth_first_search(g, boost::visitor(vis)); // Perform DFS traversal

  return 0;
}

Explanation of the Code

  • Creating the Graph: We create an instance of MyGraph called g. We then add edges specifying connections between vertices.
  • Executing DFS: By creating an instance of MyVisitor, we pass it as a visitor to depth_first_search, which traverses the graph and calls discover_vertex for each vertex.

Conclusion

Using the Boost library to create and traverse a graph can significantly simplify complex tasks in C++. By following the steps outlined above, you can successfully implement Depth First Search (DFS) on an undirected graph.

The practical application of graphs is extensive, and understanding DFS is essential for anyone looking to delve deeper into graph algorithms. Experiment with this code and modify the graph structure to best fit your needs!