接受用户定义数据类型的输入

Question

我正在编写一个程序来实现 Dijkstra 算法（图中一个节点与每个其他节点之间的最短路径）。我希望将用户作为输入给出的源节点读取为顶点（用户定义的数据类型）。

以下是我的程序：

import java.util.*;

class Vertex implements Comparable<Vertex>
{
    public final String name;
    public Edge[] adjacencies;
    public double minDistance = Double.POSITIVE_INFINITY;
    public Vertex previous;

    public Vertex(String argName) { 
        name = argName;
    }

    public String toString() {
        return name;
    }

    public int compareTo(Vertex other) {
        return Double.compare(minDistance, other.minDistance);
    }
}

class Edge
{
    public final Vertex target;
    public final double weight;

    public Edge(Vertex argTarget, double argWeight) { 
        target = argTarget;
        weight = argWeight;
    }
}

public class DijExample
{
    public static void computePaths(Vertex source) {
        /*This function computes the shortest distance*/
    }

    public static List<Vertex> getShortestPathTo(Vertex target){

        /*This function computes the shortest path*/
    }

    public static void main(String[] args){

        in = new Scanner(System.in);
        String sn;

        Vertex v0 = new Vertex("S");
        Vertex v1 = new Vertex("A");
        Vertex v2 = new Vertex("B");
        Vertex v3 = new Vertex("C");
        Vertex v4 = new Vertex("D");
        Vertex v5 = new Vertex("E");
        Vertex v6 = new Vertex("F");
        Vertex v7 = new Vertex("G");
        Vertex v8 = new Vertex("H");
        Vertex v9 = new Vertex("I");
        Vertex v10 = new Vertex("J");
        Vertex v11 = new Vertex("K");
        Vertex v12 = new Vertex("L");


        v0.adjacencies = new Edge[]{new Edge(v1,5),new Edge(v2,7),new Edge(v3,1),new Edge(v4,3),new Edge(v5,2),new Edge(v6,6)};
        v1.adjacencies = new Edge[]{new Edge(v0,5),new Edge(v5,4),new Edge(v6,7)};
        v2.adjacencies = new Edge[]{new Edge(v0,7),new Edge(v10,6),new Edge(v11,2)};
        v3.adjacencies = new Edge[]{new Edge(v0,1), new Edge(v11,1)};
        v4.adjacencies = new Edge[]{new Edge(v0,3),new Edge(v7,7)};
        v5.adjacencies = new Edge[]{new Edge(v0,2),new Edge(v8,5)};
        v6.adjacencies = new Edge[]{new Edge(v0,6),new Edge(v1,7),new Edge(v9,3)};
        v7.adjacencies = new Edge[]{new Edge(v4,7)};
        v8.adjacencies = new Edge[]{new Edge(v5,5)};
        v9.adjacencies = new Edge[]{new Edge(v6,3)};
        v10.adjacencies = new Edge[]{new Edge(v2,6),new Edge(v11,8),new Edge(v12,1)};
        v11.adjacencies = new Edge[]{new Edge(v2,2),new Edge(v3,1),new Edge(v10,8),new Edge(v12,3)};
        v12.adjacencies = new Edge[]{new Edge(v10,1),new Edge(v11,3)};

        Vertex[] vertices = { v0,v1,v2,v3,v4,v5,v6,v7,v8,v9,v10,v11,v12 };

        System.out.println("Enter the source node");
        sn = in.next();//Here sn is read as a string but I want to read it as a vertex

        computePaths(sn);//Calling the function to calculate the shortest path with the source node (of type vertex)

        for (Vertex v : vertices){
            System.out.println("Distance to " + v + ": " + v.minDistance);
            List<Vertex> path = getShortestPathTo(v);
            System.out.println("Path: " + path);
        }
    }
} 

Answer 1

我假设您的问题是关于将用户输入转换为自定义类型，而不是关于算法本身。 简单的答案是改变你的：

sn = in.next();

到

Vertex vn = new Vertex (in.next());

这为您提供了一个新顶点，但它不在您构建的数组中，而且您没有简单的方法来查找那里是否存在匹配的顶点。您也会受到错误输入的影响。

一个更有用的机制可能是将您的顶点集合更改为某种Map（可能是HashMap<String,Vertex>），键入Vertex.name。

您可以像 Vertices.add (v0.name, v0); 一样向其中添加 Vertex 对象

然后你可以检查用户是否指定了一个有效的顶点——返回读取一个字符串：

Vertex vn = null;
sn = in.next();


if (Vertices.contains(sn)) {
  vn = Vertices.get(sn);
} else {
  System.out.println ("That's not a vertex I know about");
  System.exit(1);
}