Dijkstra和FileInput。 爪哇

Question

我下面有這個Dijkstra算法的Java代碼。 我下載了代碼。 我想對此程序進行更改，並將數據存儲在文件中並讀入，而不是將其放入源代碼中。 最好的方法是什么？

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);
}

}
}

該代碼基於http://en.literateprograms.org/Special:Downloadcode/Dijkstra%27s_algorithm_%28Java%29 [最新訪問時間為2011年1月6日]

Answer 1

我建議您以普通圖形格式描述您的圖形。

它將是這樣的：

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，您可以解析此文件並創建Vertex和Edge對象。

這是完整的代碼：

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，您可以有條不紊地將數據存儲在文本文件中，例如在其他所有數據之間留有空格。 此后，您可以使用Java File Reader並將該文件的內容讀入數組。 一旦將其放入數組中，您就可以將數組索引傳遞到必須在代碼中添加數據的各個位置。 例如，它看起來與此類似（這里的String類型數組用於存儲文本文件中的數據。因此，您可以使用其索引將數據添加到代碼中。

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(); 
}