Question

Is there a way to handle Lists in Java as twodimensional?

The situation:
I have a graph with nodes, edges and weight per edge. Now I need a data structure to store for each node:
a) its neighbours
b) the edge’s weight for each neigbour

First I thought of creating a new class “node” with an identifyer and something like a two-dimensional array to store neighbour-identifyers and edge-weights. But the number of neighbours for each node is not given and may increase dynamically during runtime. Therefore I think two-dimensional arrays are not the way to go here.

I thought it would be possible to have in the class “node” a list like:

List<node> neighbours = new ArrayList<node>();

But obviously this only handles the neighbour nodes – not the weights of their edges.

Does anybody have a hint how to construct such a “graph” where for every node the neighbour’s identifyers and the corresponding edge weight are stored?

Thank you for reading 🙂

Answer 1

Most straight-forward is to use HashMap:

    class Edge {
// represents edge with destination node and it's weight
        private final Node node;
        private final int weight;

        Edge(Node node, int weight) {
            this.node = node;
            this.weight = weight;
        }

    }

// represents map which holds all outgoing edges keyed by source nodes.
    Map<Node, Set<Edges>> edgesByOutgoingNodes = new HashMap<Node, Set<Edges>>();