样本定向图和拓扑排序代码 [英] Sample Directed Graph and Topological Sort Code

问题描述

任何人都知道在哪里可以获得Directed Graph的示例实现和用于在有向图上执行拓扑排序的示例代码？ （最好在Java中）

解决方案

这是从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）; 
返回这个; 
} 
 @Override 
 public String toString（）{
 return name; 
} 
} 
 
 static class Edge {
 public final Node from; 
 public final Node to; 
 public Edge（Node，Node）{
 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 5 = new Node（5）; 
节点3 =新节点（3）; 
节点11 =新节点（11）; 
 Node 8 =新节点（8）; 
节点2 =新节点（2）; 
节点9 =新节点（9）; 
 Node ten = new Node（10）; 
 seven.addEdge（十一）.addEdge（八）; 
 five.addEdge（十一）; 
 three.addEdge（八）.addEdge（十）; 
 eleven.addEdge（two）.addEdge（nine）.addEdge（ten）; 
 eight.addEdge（九）.addEdge（十）; 
 
 Node [] allNodes = {七，五，三，十一，八，二，九，十}; 
 // L<  - 将包含排序元素的空列表
 ArrayList&Node L = new ArrayList< Node>（）; 
 
 // S<  - 没有进入边的所有节点的集合
 HashSet< Node> S = new HashSet< Node>（）; 
（节点n：allNodes）{
 if（n.inEdges.size（）== 0）{
 S.add（n）; 
} 
} 
 
 //而S不为空do 
 while（！S.isEmpty（））{
 //删除一个节点n从S 
 Node n = S.iterator（）。next（）; 
 S.remove（n）; 
 
 //将n插入L 
 L.add（n）;对于（Iterator< Edge> it = n.outEdges.iterator（）; it.hasNext（）;）的每个节点m，具有从n到m的边e e 
 
 // {
 //从图中删除边e e 
 Edge e = it.next（）; 
 Node m = e.to; 
 it.remove（）; //从n 
中删除边缘m.inEdges.remove（e）; //从边框中删除边框
 
 //如果m没有其他进入边缘然后插入到S 
如果（m.inEdges.isEmpty（））{
 S.add（m）; 
} 
} 
} 
 //检查所有边缘是否被删除
 boolean cycle = false; 
（节点n：allNodes）{
 if（！n.inEdges.isEmpty（））{
 cycle = true; 
 break; 
} 
} 
 if（cycle）{
 System.out.println（循环呈现，拓扑排序不可能）; 
} else {
 System.out.println（拓扑排序：+ Arrays.toString（L.toArray（）））; 
} 
} 
} 
  

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)

解决方案

Here is a simple implementation of the first algorithm from the Wikipedia page on Topological Sort:

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()));
    }
  }
}

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