示例有向图和拓扑排序代码

问题描述

有谁知道我可以在哪里获得有向图的示例实现和在有向图上执行拓扑排序的示例代码?(最好使用 Java)

Anyone know where I can obtain a sample implementation of a Directed Graph and sample code for performing a topological sort on a directed graph? (preferably in Java)

推荐答案

这里是 关于拓扑排序的维基百科页面:

import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashSet;
import java.util.Iterator;

public class Graph {

  static class Node{
    public final String name;
    public final HashSet<Edge> inEdges;
    public final HashSet<Edge> outEdges;
    public Node(String name) {
      this.name = name;
      inEdges = new HashSet<Edge>();
      outEdges = new HashSet<Edge>();
    }
    public Node addEdge(Node node){
      Edge e = new Edge(this, node);
      outEdges.add(e);
      node.inEdges.add(e);
      return this;
    }
    @Override
    public String toString() {
      return name;
    }
  }

  static class Edge{
    public final Node from;
    public final Node to;
    public Edge(Node from, Node to) {
      this.from = from;
      this.to = to;
    }
    @Override
    public boolean equals(Object obj) {
      Edge e = (Edge)obj;
      return e.from == from && e.to == to;
    }
  }

  public static void main(String[] args) {
    Node seven = new Node("7");
    Node five = new Node("5");
    Node three = new Node("3");
    Node eleven = new Node("11");
    Node eight = new Node("8");
    Node two = new Node("2");
    Node nine = new Node("9");
    Node ten = new Node("10");
    seven.addEdge(eleven).addEdge(eight);
    five.addEdge(eleven);
    three.addEdge(eight).addEdge(ten);
    eleven.addEdge(two).addEdge(nine).addEdge(ten);
    eight.addEdge(nine).addEdge(ten);

    Node[] allNodes = {seven, five, three, eleven, eight, two, nine, ten};
    //L <- Empty list that will contain the sorted elements
    ArrayList<Node> L = new ArrayList<Node>();

    //S <- Set of all nodes with no incoming edges
    HashSet<Node> S = new HashSet<Node>();
    for(Node n : allNodes){
      if(n.inEdges.size() == 0){
        S.add(n);
      }
    }

    //while S is non-empty do
    while(!S.isEmpty()){
      //remove a node n from S
      Node n = S.iterator().next();
      S.remove(n);

      //insert n into L
      L.add(n);

      //for each node m with an edge e from n to m do
      for(Iterator<Edge> it = n.outEdges.iterator();it.hasNext();){
        //remove edge e from the graph
        Edge e = it.next();
        Node m = e.to;
        it.remove();//Remove edge from n
        m.inEdges.remove(e);//Remove edge from m

        //if m has no other incoming edges then insert m into S
        if(m.inEdges.isEmpty()){
          S.add(m);
        }
      }
    }
    //Check to see if all edges are removed
    boolean cycle = false;
    for(Node n : allNodes){
      if(!n.inEdges.isEmpty()){
        cycle = true;
        break;
      }
    }
    if(cycle){
      System.out.println("Cycle present, topological sort not possible");
    }else{
      System.out.println("Topological Sort: "+Arrays.toString(L.toArray()));
    }
  }
}

这篇关于示例有向图和拓扑排序代码的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！