Dijkstra算法的文件输入

时间：2011-11-25 06:03:00

标签： java file input graph-theory dijkstra

我无法弄清楚如何用java读取输入文件。该文件具有以下格式：

u1 v1 w1
u2 v2 w2
...
um vm wm
-1
source

每个3元组表示一个边，由其源顶点，目标顶点及其权重指定（例如：newyork boston 30）。图形的描述以“标志”结束，整数为-1。字符串跟随此标志;此字符串是Dijkstra最短路径算法的源顶点的名称。也就是说，您要确定并打印出从此源顶点到图中每个其他顶点的最短路径。 这是我目前的工作。

import java.io.File;
import java.io.FileNotFoundException;
import java.util.PriorityQueue;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Scanner;

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

        Collections.reverse(path);
        return path;
    }

    public String[] readFile(String fileName) throws FileNotFoundException {
        Scanner input = new Scanner(new File(fileName));
        String line = "";
        while (input.hasNext()) {
            line = line.concat(input.nextLine());
        }
        String[] graph = line.split("");
        return graph;

    }

    public static void main(String[] args) throws FileNotFoundException {

        final String TEST = "/TestInput.txt";
        Scanner input = new Scanner(new File(TEST));
        String line = "";
        while (input.hasNext()) {
            line = line.concat(input.nextLine());
        }
        String[] graph = line.split(" ");

        for (int i = 0; i < graph.length; i++) {
            System.out.println(graph[i]);
        }

        Vertex[] verts = new Vertex[graph.length];
        Edge[] edges = new Edge[graph.length];
        Vertex v1 = new Vertex("");
        Vertex v2 = new Vertex("");
        Vertex source = new Vertex("");
        int count = 0;

        outerloop: for (int i = 0; i < (graph.length); i++) {

            if (graph[i].equals("-1")) {
                // do algorithm initialization here w/ source
            }
            if (i == 0) {
                verts[i] = new Vertex(graph[i]);
                count++;
            } else {
                innerloop: for (int j = count; j >= 0; j--) {
                    if (i / 3 == 0) {

                        if (graph[i].equals(verts[j].toString())) {
                            break innerloop;
                        } else if (j == 0) {
                            verts[count] = new Vertex(graph[i]);
                            v1 = verts[count];
                            count++;
                        }
                    }

                    if (i / 3 == 1) {

                        if (graph[i].equals(verts[j])) {
                            break innerloop;
                        } else if (j == 0) {
                            verts[count] = new Vertex(graph[i]);
                            v2 = verts[count];
                            count++;
                        }
                    }
                    if (i / 3 == 2) {

                    }
                }
            }

        }

        for (int i = 0; i < verts.length; i++) {
            System.out.println(verts[i]);
        }
    }
}

所以我唯一的问题是如何从给定的.txt文件格式到图形。欢迎任何建议。

3 个答案:

答案 0 :(得分：2)

使用Scanner解析文件数据。对于每个元组，如果尚未创建源顶点，则创建它，否则在预先存在的图中找到它 - 创建搜索功能。对目标顶点执行相同操作。接下来，创建一个权重等于元组中第三个标记的边，并将目标顶点添加到边。最后，将边添加到源顶点的邻接列表中。

对于前面提到的搜索功能，您可以实现一些可以从任何顶点开始搜索图形的每个顶点的东西。递归是必要的。

public static Vertex search(Vertex src, String name);

更简单的解决方案是保留您创建的所有顶点的列表，以构建图形并搜索它。

public static Vertex search(List<Vertex> vertices, String name);

当您完成构建图形并且您具有Dijkstra算法将开始的顶点的名称时，您可以使用搜索函数来获取对顶点的引用。

Dijkstra.computePath(search(vertices, startVertexName));

而且就是这样。以下是如何解析文件数据的示例：

List<Vertex> vertices = new ArrayList<Vertex>();
String src = 
    "Pittsburgh Philadelphia 323 "+
    "Pittsburgh Ohio 125 "+
    "Ohio Philadelphia 400 "+
    "-1 Ohio";
            //new Scanner(new File(fileName));
Scanner scnr = new Scanner(src); 
String src, target;
int weight;
while(scnr.hasNext())
{
    src = scnr.next();
    if(src.equals("-1"))
        break;
    else {
        target = scnr.next();
        weight = scnr.nextInt();
    }
    //call search(), implement logic in addToGraph()
    addVertexToGraph(src, target, weight, vertices);    
}   
String startVertexName = scnr.next();
scnr.close();

请注意Scanner.next返回由空格分隔的下一个标记（默认分隔符），因此您的文件数据必须以这种方式格式化。

答案 1 :(得分：0)

这是一个镜头：

/**
 * Read the file using provided filename, construct vertices etc.
 * 
 * @param fileName name of the file to read.
 * @return true if everything is OK
 * @throws FileNotFoundException if file is not found or not readable
 */
public boolean readFile(final String fileName) throws FileNotFoundException {
    final Scanner input = new Scanner(new File(fileName));
    boolean result = false;

    while (input.hasNext()) {
        final String line = line = input.nextLine();
        if ("-1".equals(line)) {
            // end of data
            if (input.hasNext()) {
                final String nameOfTheSource = input.next();
                // TODO: do something with nameOfTheSource
                result = true;
            } else {
                // bad input format: there should be something after -1
            }
        } else {
            final String Scanner vert = new Scanner(line);

            try {
                final String sourceName = vert.next();
                final String targetName = vert.next();
                final int weight = vert.nextInt(); // assuming int for weight
                // TODO: create Vertices and Edge here
            } catch (final NoSuchElementException ex) {
                // bad input format for "line"!
            }
        }
    }

    return result;
}

未经测试。

答案 2 :(得分：0)

{{import Stack.Dijkstra; { import java.io.File; {{import java.io.FileNotFoundException; {导入java.util.Scanner;

{{public class App { { public static void main（String [] args）引发{FileNotFoundException { { Vertex v1 = new Vertex（“ A”）;         {Vertex v2 = new Vertex("B"); {顶点v3 =新的顶点（“ C”）; 

    {`v1.addNeighbour(new Edge(1, v1, v2));
    {`v1.addNeighbour(new Edge(10, v1, v2));
    {`v2.addNeighbour(new Edge(1, v2, v3));

    {`Dijkstra dijkstra = new Dijkstra();
    {`dijkstra.computePath(v1);

    {`System.out.println(dijkstra.getShortestPathTo(v3));
    {`final String test = "X:\\neon3\\eclipse\\TestInput.txt";
    {`Scanner input = new Scanner(new File(test));
    {`String line = "";
    {`while (input.hasNext()) {
        {`line = line.concat(input.nextLine());
    }
    {`String[] graph = line.split(" ");

    {`for (int i = 0; i < graph.length; i++) {
        {`System.out.println(graph[i]);
    }
}

}`}

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