Java - Which is the best implementation structure for Graph?

Question

The graph is very large but undirected. Edges are unweighted.

In my implementation, I have to find the vertex with max degree and do deletion on both vertexes and edges.

Answer 1

My suggestion would be to store the vertexes in a priority queue. That way you can have very fast access to the vertex with the highest degree. As for how to implement the vertexes, I would store each neighboring vertex in some kind of set data-structure such as a HashSet or a TreeSet to be able to remove stuff efficiently. I wouldn't represent the edges explicitly, it's not needed.

Code, something along the lines of:

class Graph {

  PriorityQueue vertexes;

  public Graph() {
    vertexes = new PriorityQueue(10,new Vertex());
  }

  public Vertex maxDegreeVertex() {
    return vertexes.peek();
  }

  ...

}

class Vertex implements Comparator {
  HashSet edges;

  public Vertex() {
    edges = new HashSet();
  }

  public compare(Vertex v1, Vertex v2) {
    v2.edges.size().compareTo(v1.edges.size());
  }

  ...

}

Hope this helps.