Java:for循环中的对象数组赋值

Question

我正在尝试使用 Dijkstra 算法找到从特定顶点 (v0) 到其余顶点的最短路径。这已解决，并且适用于以下链接中的此代码:http://en.literateprograms.org/index.php?title=Special:DownloadCode/Dijkstra%27s_algorithm_(Java)&oldid=15444

我在从用户输入的 for 循环中分配 Edge 数组时遇到问题，而不是像这里那样对其进行硬编码。

从每个顶点向 Edge[] 邻接分配一条新边有什么帮助吗？请记住，它可以是 1 个或多个边。

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 static void main(String[] args)
{
    Vertex v[] = new Vertex[3];
    Vertex v[0] = new Vertex("Harrisburg");
    Vertex v[1] = new Vertex("Baltimore");
    Vertex v[2] = new Vertex("Washington");

    v0.adjacencies = new Edge[]{ new Edge(v[1],  1),
                             new Edge(v[2],  3) };
    v1.adjacencies = new Edge[]{ new Edge(v[0], 1),
                             new Edge(v[2],  1),};
    v2.adjacencies = new Edge[]{ new Edge(v[0],  3),
                                 new Edge(v[1],  1)  };

    Vertex[] vertices = { v0, v1, v2};
       /*Three vertices with weight: V0 connects (V1,1),(V2,3)
                                     V1 connects (V0,1),(V2,1)
                                     V2 connects (V1,1),(V2,3)
       */  
    computePaths(v0);
    for (Vertex v : vertices){
    System.out.println("Distance to " + v + ": " + v.minDistance);
    List<Vertex> path = getShortestPathTo(v);
    System.out.println("Path: " + path);
    }
}
}

上面的代码可以很好地找到从 v0 到所有其他顶点的最短路径。将新的 edge[] 分配给 edge[] 邻接时会出现问题。

例如，这不会产生正确的输出:

for (int i = 0; i < total_vertices; i++){
        s = br.readLine();
        char[] line = s.toCharArray();
        for (int j = 0; j < line.length; j++){  
           if(j % 4 == 0 ){ //Input: vertex weight vertex weight: 1 1 2 3
            int vert = Integer.parseInt(String.valueOf(line[j]));
            int w = Integer.parseInt(String.valueOf(line[j+2]));
            v[i].adjacencies = new Edge[] {new Edge(v[vert], w)};
        }
        }
    }

与此相反:

v0.adjacencies = new Edge[]{ new Edge(v[1],  1),
                         new Edge(v[2],  3) };

我如何获取用户输入并制作一个 Edge[]，以将其传递给邻接点？问题是它可能是 0 个边或很多边。

任何帮助将不胜感激 谢谢!

Answer 1

在您的情况下，您为 j 的每次迭代分配 v[i].adjacencies...所以这意味着它 line.length = 8，然后 v[i].adjacencies 被分配 2 次。我不认为那是你的意图。

    for (int j = 0; j < line.length; j++){  
       if(j % 4 == 0 ){ //Input: vertex weight vertex weight: 1 1 2 3
        int vert = Integer.parseInt(String.valueOf(line[j]));
        int w = Integer.parseInt(String.valueOf(line[j+2]));
        v[i].adjacencies = new Edge[] {new Edge(v[vert], w)};
    }

您可以像这样更改您的代码...

    Edge[] edges = new Edge[line.length/4];  
    for (int j = 0; j < line.length; j++){           
       if(j % 4 == 0 ){ //Input: vertex weight vertex weight: 1 1 2 3
        int vert = Integer.parseInt(String.valueOf(line[j]));
        int w = Integer.parseInt(String.valueOf(line[j+2]));
        edges[j/4] =  {new Edge(v[vert], w)};
    }
   v[i].adjacencies = edges;

它可能不是确切的代码，但你必须在循环外分配。