import java.util.LinkedList;
import java.util.HashMap;

public class Graph {

// Each node maps to a list of all his neighbors
private HashMap<Node, LinkedList<Node>> adjacencyMap;
private boolean directed;

public Graph(boolean directed) {
    this.directed = directed;
    adjacencyMap = new HashMap<>();
}

public void addEdgeHelper(Node a, Node b) {
    LinkedList<Node> tmp = adjacencyMap.get(a);

    if (tmp != null) {
        tmp.remove(b);
    }
    else tmp = new LinkedList<>();
    tmp.add(b);
    adjacencyMap.put(a,tmp);
}

public void addEdge(Node source, Node destination) {

    // We make sure that every used node shows up in our .keySet()
    if (!adjacencyMap.keySet().contains(source))
        adjacencyMap.put(source, null);

    if (!adjacencyMap.keySet().contains(destination))
        adjacencyMap.put(destination, null);

    addEdgeHelper(source, destination);

    // If a graph is undirected, we want to add an edge from destination to source as well
    if (!directed) {
        addEdgeHelper(destination, source);
    }
}


public void printEdges() {
        for (Node node : adjacencyMap.keySet()) {
            System.out.print("The " + node.name + " has an edge towards: ");
            if (adjacencyMap.get(node) != null) {
                for (Node neighbor : adjacencyMap.get(node)) {
                    System.out.print(neighbor.name + " ");
                }
                System.out.println();
            }
            else {
                System.out.println("none");
            }
        }
    }

public boolean hasEdge(Node source, Node destination) {
    return adjacencyMap.containsKey(source) && adjacencyMap.get(source) != null && adjacencyMap.get(source).contains(destination);
    }
}