在Java实现通用图

我们已经了解了Java的泛型类。我们还可以使用它们在Java为 Graph 编码。 Graph 类是使用Java的HashMap 实现的。正如我们所知 HashMap 包含一个键和一个值，我们将节点表示为键及其在图中的值中的邻接列表。

示例：具有 5 个顶点的无向无权图。

邻接矩阵：

邻接表：

方法：
与 C++ 一样，我们在创建泛型类时使用 <> 来指定参数类型。要创建泛型类的对象，我们使用以下语法。

// To create an instance of generic class 
BaseType  obj = new BaseType ()

Note: In Parameter type, we cannot use primitives like 
      'int','char' or 'double'.

下面是上述方法的实现：

// Java program to implement Graph
// with the help of Generics
  
import java.util.*;
  
class Graph {
  
    // We use Hashmap to store the edges in the graph
    private Map > map = new HashMap<>();
  
    // This function adds a new vertex to the graph
    public void addVertex(T s)
    {
        map.put(s, new LinkedList());
    }
  
    // This function adds the edge
    // between source to destination
    public void addEdge(T source,
                        T destination,
                        boolean bidirectional)
    {
  
        if (!map.containsKey(source))
            addVertex(source);
  
        if (!map.containsKey(destination))
            addVertex(destination);
  
        map.get(source).add(destination);
        if (bidirectional == true) {
            map.get(destination).add(source);
        }
    }
  
    // This function gives the count of vertices
    public void getVertexCount()
    {
        System.out.println("The graph has "
                           + map.keySet().size()
                           + " vertex");
    }
  
    // This function gives the count of edges
    public void getEdgesCount(boolean bidirection)
    {
        int count = 0;
        for (T v : map.keySet()) {
            count += map.get(v).size();
        }
        if (bidirection == true) {
            count = count / 2;
        }
        System.out.println("The graph has "
                           + count
                           + " edges.");
    }
  
    // This function gives whether
    // a vertex is present or not.
    public void hasVertex(T s)
    {
        if (map.containsKey(s)) {
            System.out.println("The graph contains "
                               + s + " as a vertex.");
        }
        else {
            System.out.println("The graph does not contain "
                               + s + " as a vertex.");
        }
    }
  
    // This function gives whether an edge is present or not.
    public void hasEdge(T s, T d)
    {
        if (map.get(s).contains(d)) {
            System.out.println("The graph has an edge between "
                               + s + " and " + d + ".");
        }
        else {
            System.out.println("The graph has no edge between "
                               + s + " and " + d + ".");
        }
    }
  
    // Prints the adjancency list of each vertex.
    @Override
    public String toString()
    {
        StringBuilder builder = new StringBuilder();
  
        for (T v : map.keySet()) {
            builder.append(v.toString() + ": ");
            for (T w : map.get(v)) {
                builder.append(w.toString() + " ");
            }
            builder.append("\n");
        }
  
        return (builder.toString());
    }
}
  
// Driver Code
public class Main {
  
    public static void main(String args[])
    {
  
        // Object of graph is created.
        Graph g = new Graph();
  
        // edges are added.
        // Since the graph is bidirectional,
        // so boolean bidirectional is passed as true.
        g.addEdge(0, 1, true);
        g.addEdge(0, 4, true);
        g.addEdge(1, 2, true);
        g.addEdge(1, 3, true);
        g.addEdge(1, 4, true);
        g.addEdge(2, 3, true);
        g.addEdge(3, 4, true);
  
        // print the graph.
        System.out.println("Graph:\n"
                           + g.toString());
  
        // gives the no of vertices in the graph.
        g.getVertexCount();
  
        // gives the no of edges in the graph.
        g.getEdgesCount(true);
  
        // tells whether the edge is present or not.
        g.hasEdge(3, 4);
  
        // tells whether vertex is present or not
        g.hasVertex(5);
    }
}

输出：

Graph:
0: 1 4 
1: 0 2 3 4 
2: 1 3 
3: 1 2 4 
4: 0 1 3 

The graph has 5 vertex
The graph has 7 edges.
The graph has an edge between 3 and 4.
The graph does not contain 5 as a vertex.

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