Dijkstra 和 FileInput。爪哇

Question

我下面有这个 Dijkstra 算法的 java 代码。我下载了代码。我想对此程序进行更改并将数据存储在文件中并读取它而不是将其放入源代码中。做到这一点的最佳方法是什么？

import java.util.PriorityQueue;
import java.util.List;
import java.util.ArrayList;
import java.util.Collections;


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 Dijkstra
{
public static void computePaths(Vertex source)
{
    source.minDistance = 0.;
    PriorityQueue<Vertex> vertexQueue = new PriorityQueue<Vertex>();
    vertexQueue.add(source);

while (!vertexQueue.isEmpty()) {
    Vertex u = vertexQueue.poll();

        // Visit each edge exiting u
        for (Edge e : u.adjacencies)
        {
            Vertex v = e.target;
            double weight = e.weight;
            double distanceThroughU = u.minDistance + weight;
    if (distanceThroughU < v.minDistance) {
        vertexQueue.remove(v);

        v.minDistance = distanceThroughU ;
        v.previous = u;
        vertexQueue.add(v);

    }

        }
    }
}


public static List<Vertex> getShortestPathTo(Vertex target)
{
    List<Vertex> path = new ArrayList<Vertex>();
    for (Vertex vertex = target; vertex != null; vertex = vertex.previous)
        path.add(vertex);
        Collections.reverse(path);
        return path;
}

public static void main(String[] args)
{
Vertex v0 = new Vertex("Nottinghill_Gate");
Vertex v1 = new Vertex("High_Street_kensignton");
Vertex v2 = new Vertex("Glouchester_Road");
Vertex v3 = new Vertex("South_Kensignton");
Vertex v4 = new Vertex("Sloane_Square");
Vertex v5 = new Vertex("Victoria");
Vertex v6 = new Vertex("Westminster");
v0.adjacencies = new Edge[]{new Edge(v1,  79.83), new Edge(v6,  97.24)};
v1.adjacencies = new Edge[]{new Edge(v2,  39.42), new Edge(v0, 79.83)};
v2.adjacencies = new Edge[]{new Edge(v3,  38.65), new Edge(v1, 39.42)};
v3.adjacencies = new Edge[]{new Edge(v4, 102.53), new Edge(v2,  38.65)};
v4.adjacencies = new Edge[]{new Edge(v5, 133.04), new Edge(v3, 102.53)};
v5.adjacencies = new Edge[]{new Edge(v6,  81.77), new Edge(v4, 133.04)};
v6.adjacencies = new Edge[]{new Edge(v0,  97.24), new Edge(v5, 81.77)};
Vertex[] vertices = { v0, v1, v2, v3, v4, v5, v6 };


    computePaths(v0);
    for (Vertex v : vertices)
{
    System.out.println("Distance to " + v + ": " + v.minDistance);
    List<Vertex> path = getShortestPathTo(v);
    System.out.println("Path: " + path);
}

}
}

该代码基于 http://en.literateprograms.org/Special：下载代码/Dijkstra%27s_algorithm_%28Java%29 [最后访问时间：2011 年 1 月 6 日]

Answer 1

我建议使用简单图表格式描述您的图表。

它看起来像这样：

v0 Harrisburg
v1 Baltimore
v2 Washington
v3 Philadelphia
v4 Binghamton
v5 Allentown
v6 New York
#
v0 v1 79.83
v0 v5 81.15
v1 v0 79.75
v1 v2 39.42
v1 v3 103.00
v2 v1 38.65
v3 v1 102.53
v3 v5 61.44
v3 v6 96.79
v4 v5 133.04
v5 v0 81.77
v5 v3 62.05
v5 v4 134.47
v5 v6 91.63
v6 v3 97.24
v6 v5 87.94

然后您可以解析该文件并创建顶点和边对象。

这是完整的代码：

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

    public Vertex(String argName) {
        name = argName;
        adjacencies = new ArrayList<Edge>();
    }

    public void addEdge(Edge e) {
        adjacencies.add(e);
    }

    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 Dijkstra {

    public static void computePaths(Vertex source) {
        source.minDistance = 0.;
        PriorityQueue<Vertex> vertexQueue = new PriorityQueue<Vertex>();
        vertexQueue.add(source);

        while (!vertexQueue.isEmpty()) {
            Vertex u = vertexQueue.poll();

            // Visit each edge exiting u

            for (Edge e : u.adjacencies) {
                Vertex v = e.target;
                double weight = e.weight;
                double distanceThroughU = u.minDistance + weight;
                if (distanceThroughU < v.minDistance) {
                    vertexQueue.remove(v);
                    v.minDistance = distanceThroughU;
                    v.previous = u;
                    vertexQueue.add(v);
                }

            }
        }
    }

    public static List<Vertex> getShortestPathTo(Vertex target) {
        List<Vertex> path = new ArrayList<Vertex>();
        for (Vertex vertex = target; vertex != null; vertex = vertex.previous)
            path.add(vertex);

        Collections.reverse(path);
        return path;
    }

    public static void main(String args[]) {

        Map<String, Vertex> vertexMap = new HashMap<String, Vertex>();
        BufferedReader in = null;
        try {
            in = new BufferedReader(new FileReader("graph.txt"));
            String line;
            boolean inVertex = true;

            while ((line = in.readLine()) != null) {
                if (line.charAt(0) == '#') {
                    inVertex = false;
                    continue;
                }
                if (inVertex) {
                    //store the vertices
                    int indexOfSpace = line.indexOf(' ');
                    String vertexId = line.substring(0, indexOfSpace);
                    String vertexName = line.substring(indexOfSpace + 1);
                    Vertex v = new Vertex(vertexName);
                    vertexMap.put(vertexId, v);
                } else {
                    //store the edges
                    String[] parts = line.split(" ");
                    String vFrom = parts[0];
                    String vTo = parts[1];
                    double weight = Double.parseDouble(parts[2]);
                    Vertex v = vertexMap.get(vFrom);
                    if (v != null) {
                        v.addEdge(new Edge(vertexMap.get(vTo), weight));
                    }
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
            return;
        }
        finally{
            if(in!= null)
                try {
                    in.close();
                } catch (IOException ignore) {
                }
        }

        //get a list of all the vertices
        Collection<Vertex> vertices = vertexMap.values();
        Vertex source = vertices.iterator().next();
        System.out.println("Computing paths from " + source);
        computePaths(source);
        for (Vertex v : vertices) {
            System.out.println("Distance to " + v + ": " + v.minDistance);
            List<Vertex> path = getShortestPathTo(v);
            System.out.println("Path: " + path);
        }
    }
}

Answer 2

基本上，您可以以有条理的方式将数据存储在文本文件中，例如在每个其他数据之间留一个空格。此后，您可以使用 Java 文件读取器并将该文件的内容读取到数组中。一旦它进入数组，您就可以将数组索引传递到必须在代码中添加数据的相应位置。
例如，它看起来与此类似，（这里 String 类型数组用于存储文本文件中的数据。因此，您可以使用其索引将数据添加到代码中。

FileInputStream fileinputstream = new FileInputStream("FileName.txt");
DataInputStream datainputstream = new DataInputStream(fileinputstream);
BufferedReader bufferedreader1 = new BufferedReader(new InputStreamReader(datainputstream));                                    
do{
   String s1;
   if((s1 = bufferedreader1.readLine()) == null){
       break;
  }
       String as[] = s1.split(" "); 
} while(true);
   datainputstream.close(); 
}