How to write a graph search algorithm using C#

How to use C# to write a graph search algorithm

The graph search algorithm is one of the important algorithms in computer science. It is widely used in website search engines and social networks relationship analysis, recommendation systems and other fields. In this article, we will introduce how to write graph search algorithms using C# and provide specific code examples.

First, we need to define a graph data structure. In C#, we can use adjacency lists or adjacency matrices to represent graphs. An adjacency list is a data structure used to represent sparse graphs that uses an array to store vertices, and each vertex has a linked list to store its adjacent vertices. An adjacency matrix is ​​a data structure used to represent dense graphs, which uses a two-dimensional array to record the relationship between every two vertices.

The following is a C# code example that uses an adjacency list to represent a graph:

class Graph
{
    int V; // 图的顶点数目
    List<int>[] adj; // 存储邻接表
    
    public Graph(int v)
    {
        V = v;
        adj = new List<int>[V];
        for (int i = 0; i < V; ++i)
        {
            adj[i] = new List<int>();
        }
    }
    
    public void AddEdge(int v, int w)
    {
        adj[v].Add(w);
        adj[w].Add(v);
    }
    
    public void BFS(int s)
    {
        bool[] visited = new bool[V];
        Queue<int> queue = new Queue<int>();
        
        visited[s] = true;
        queue.Enqueue(s);
        
        while (queue.Count != 0)
        {
            s = queue.Dequeue();
            Console.Write(s + " ");
            
            foreach (int i in adj[s])
            {
                if (!visited[i])
                {
                    visited[i] = true;
                    queue.Enqueue(i);
                }
            }
        }
    }
}

In the above code, we define a Graph class, which contains a constructor, AddEdge method and BFS method. The constructor is used to initialize the number of vertices and adjacency list of the graph. The AddEdge method is used to add edges, and the BFS method is used to perform breadth-first search.

Next, we can use the above code to create a graph and perform a breadth-first search as follows:

class Program
{
    static void Main(string[] args)
    {
        Graph g = new Graph(4);
        
        g.AddEdge(0, 1);
        g.AddEdge(0, 2);
        g.AddEdge(1, 2);
        g.AddEdge(2, 0);
        g.AddEdge(2, 3);
        g.AddEdge(3, 3);
        
        Console.WriteLine("广度优先搜索结果为：");
        g.BFS(2);
    }
}

The above code creates a graph with 4 vertices and adds Some sides. Then, we perform a breadth-first search and output the results.

In addition to breadth-first search, there are other graph search algorithms, such as depth-first search, Dijkstra algorithm, Bellman-Ford algorithm, etc. These algorithms have important applications in graph theory. You can extend the sample code we provide as needed.

To summarize, this article introduces how to use C# to write a graph search algorithm and how to use adjacency lists to represent graphs. We provide concrete code examples and use breadth-first search to illustrate the execution of the algorithm. I hope this article helps you understand graph search algorithms.

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