使用有向图实现Dijkstra算法

Question

我试图通过邻接表使用有向图来实现Dijkstra的算法。 我找到了一些示例代码。 在该代码中，图形的填充如下：

private static final Graph.Edge[] GRAPH = {
    new Graph.Edge("a", "b", 7),
    new Graph.Edge("a", "c", 9),
    new Graph.Edge("a", "f", 14),
    new Graph.Edge("b", "c", 10),
    new Graph.Edge("b", "d", 15),
    new Graph.Edge("c", "d", 11),
    new Graph.Edge("c", "f", 2),
   new Graph.Edge("d", "e", 6),
    new Graph.Edge("e", "f", 9),};
private static final String START = "a";
private static final String END = "e";

由于我需要从文本文件的邻接列表中进行填充，因此我尝试以这种方式进行填充：

List<Graph.Edge> list = new ArrayList<>();

    try {
        Scanner scanner = new Scanner(new File(filename));
        while (scanner.hasNextLine()) {
            String source = scanner.findInLine(NAME);
            if (source != null) {
                while (true) {
                    String to = scanner.findInLine(NAME);
                    if (to == null) {
                        break;
                    }
                    int weight = Integer.valueOf(scanner.findInLine(WEIGHT));
                    list.add(new Graph.Edge(source, to, weight));
                }
            }
            scanner.nextLine();
        }
    } catch (FileNotFoundException | NumberFormatException e) {
    }

与

static final Pattern NAME = Pattern.compile("\\w+");
static final Pattern WEIGHT = Pattern.compile("\\d+");

在示例代码中，他们然后通过以下方式在图上运行dijkstra的算法：

Graph g = new Graph(GRAPH);
    g.dijkstra(START);
    g.printPath(END);
    g.printAllPaths();

我尝试更新代码以实现该算法的实现。 我想出了以下几点：

try {
        Scanner scanner = new Scanner(new File(filename));

        while (scanner.hasNextLine()) {
            String source = scanner.findInLine(NAME);
            if (source != null) {
                while (true) {
                    String go = scanner.findInLine(NAME);
                    if (go == null) {
                        break;
                    }
                    int weight = Integer.valueOf(scanner.findInLine(WEIGHT));
                    Graph.Edge edge = new Graph.Edge(source, go, weight);

                    Graph g = new Graph(GRAPH);
                    g.dijkstra(source);
                    g.printPath(go);
                }
            }

            scanner.nextLine();
        }
    } catch (FileNotFoundException | NumberFormatException e) {
    }

当我尝试运行它时，似乎无法正确填充我的图形。 它通过dijkstra和printPath方法产生错误，指出“图形不包含起始/终止顶点”。 如何更新代码，以便正确填充图形并能够正确实现算法？ 谢谢！

编辑：这是我的输入文件的示例

1 2 1 3 1
2 4 2
3 2 2 5 4
4 3 3 5 3
5 1 4

它遵循格式源adj。 顶点，重量，调整 顶点，重量...

编辑2：使用Graph.Edge`

class Graph {

private final Map<String, Vertex> graph; // mapping of vertex names to Vertex objects, built from a set of Edges

/**
 * One edge of the graph (only used by Graph constructor)
 */
public static class Edge {

    public final String v1, v2;
    public final int dist;

    public Edge(String v1, String v2, int dist) {
        this.v1 = v1;
        this.v2 = v2;
        this.dist = dist;
    }
}

和

public Graph(Edge[] edges) {
    graph = new HashMap<>(edges.length);

    //one pass to find all vertices
    for (Edge e : edges) {
        if (!graph.containsKey(e.v1)) {
            graph.put(e.v1, new Vertex(e.v1));
        }
        if (!graph.containsKey(e.v2)) {
            graph.put(e.v2, new Vertex(e.v2));
        }
    }

    //another pass to set neighbouring vertices
    for (Edge e : edges) {
        graph.get(e.v1).neighbours.put(graph.get(e.v2), e.dist);
        //graph.get(e.v2).neighbours.put(graph.get(e.v1), e.dist); // also do this for an undirected graph
    }
}

编辑：在这里我从http://rosettacode.org/wiki/Dijkstra%27s_algorithm#Java找到原始的示例代码

Answer 1

为了将应用程序与文件输入一起使用 ，请使用第一个文件输入算法 。 除非您想将文件的每一行作为仅带有一个Vertex的Graph来运行，否则第二种算法是没有用的。

像这样使用您的代码（我在更改的行上加上了注释）：

private static final Graph.Edge[] GRAPH = getEdges("input.txt"); // <-- CHANGED THIS
private static final String START = "1"; // <-- CHANGED THIS
private static final String END = "5"; // <-- CHANGED THIS

private static Graph.Edge[] getEdges(String fileName) { // <-- ADDED THIS
    final Pattern NAME = Pattern.compile("\\w+");
    final Pattern WEIGHT = Pattern.compile("\\d+");
    List<Graph.Edge> list = new ArrayList<>();
    try {
        Scanner scanner = new Scanner(new File(fileName));
        while (scanner.hasNextLine()) {
            String source = scanner.findInLine(NAME);
            if (source != null) {
                while (true) {
                    String to = scanner.findInLine(NAME);
                    if (to == null) {
                        break;
                    }
                    int weight = Integer.valueOf(scanner.findInLine(WEIGHT));
                    list.add(new Graph.Edge(source, to, weight));
                }
            }
            if (scanner.hasNextLine()) // <-- ADDED THIS
                scanner.nextLine();
        }
    } catch (FileNotFoundException | NumberFormatException e) {
    }
    return list.toArray(new Graph.Edge[0]); // <-- ADDED THIS
}

然后，以相同方式运行应用程序：

Graph g = new Graph(GRAPH);
g.dijkstra(START);
g.printPath(END);
g.printAllPaths();

我测试了所有这些，还发现您的文件输入算法在文件的最后一行中断，因此我if (scanner.hasNextLine())之前添加了if (scanner.hasNextLine()) scanner.nextLine();