src/com.example.portfolio3/com/example/portfolio3/AdjListGraph.java



package com.example.portfolio3;

// origin: <https://moodle.ruc.dk/course/section.php?id=211877>

import java.util.Collection;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;

/// Adjecency List Graph - A map from vertices
/// to set of outedges from the vertex
public class AdjListGraph extends AbstractGraph {

    /// foo
    public AdjListGraph() { }

    /// foo
    private Map<Vertex, Set<Edge>> outEdge = new HashMap<>();

    /// foo
    public final void insertEdge(
        final Vertex v1, final Vertex v2, final int w
    ) {
        Edge e = new Edge(v1, v2, w);
        if (!outEdge.containsKey(e.from())) {
            outEdge.put(e.from(), new HashSet<Edge>());
        }
        outEdge.get(e.from()).add(e);
    }

    /// foo
    public final Collection<Edge> edges() {
        Set<Edge> edges = new HashSet<>();
        for (Vertex v: outEdge.keySet()) {
            edges.addAll(outEdge.get(v));
        }

        return edges;
    }

    /// foo
    public final Collection<Edge> outEdge(final Vertex v) {
        if (!outEdge.containsKey(v)) {
            return new HashSet<Edge>();
        }

        return outEdge.get(v);
    }

    /// foo
    public final Integer getWeight(
        final Vertex v1, final Vertex v2
    ) {

        // linear in number of outedges from vertices
        if (!outEdge.containsKey(v1)) {
            return null;
        }
        for (Edge e: outEdge.get(v1)) {
            if (e.to() == v2) {
                return e.weight();
            }
        }

        return null;
    }
}