import java.util.*;

/**
 * A representation of a graph.
 * Assumes that we do not have negative cost edges in the graph.
 */
public class MyGraph implements Graph {
    // you will need some private fields to represent the graph
    // you are also likely to want some private helper methods

    // YOUR CODE HERE

    /**
     * Creates a MyGraph object with the given collection of vertices
     * and the given collection of edges.
     * @param v a collection of the vertices in this graph
     * @param e a collection of the edges in this graph
     */
    public MyGraph(Collection<Vertex> v, Collection<Edge> e) {

	// YOUR CODE HERE

    }

    /** 
     * Return the collection of vertices of this graph
     * @return the vertices as a collection (which is anything iterable)
     */
    public Collection<Vertex> vertices() {

	// YOUR CODE HERE

    }

    /** 
     * Return the collection of edges of this graph
     * @return the edges as a collection (which is anything iterable)
     */
    public Collection<Edge> edges() {

	// YOUR CODE HERE

    }

    /**
     * Return a collection of vertices adjacent to a given vertex v.
     *   i.e., the set of all vertices w where edges v -> w exist in the graph.
     * Return an empty collection if there are no adjacent vertices.
     * @param v one of the vertices in the graph
     * @return an iterable collection of vertices adjacent to v in the graph
     * @throws IllegalArgumentException if v does not exist.
     */
    public Collection<Vertex> adjacentVertices(Vertex v) {

	// YOUR CODE HERE

    }

    /**
     * Test whether vertex b is adjacent to vertex a (i.e. a -> b) in a directed graph.
     * Assumes that we do not have negative cost edges in the graph.
     * @param a one vertex
     * @param b another vertex
     * @return cost of edge if there is a directed edge from a to b in the graph, 
     * return -1 otherwise.
     * @throws IllegalArgumentException if a or b do not exist.
     */
    public int edgeCost(Vertex a, Vertex b) {

	// YOUR CODE HERE

    }

    /**
     * Returns the shortest path from a to b in the graph, or null if there is
     * no such path.  Assumes all edge weights are nonnegative.
     * Uses Dijkstra's algorithm.
     * @param a the starting vertex
     * @param b the destination vertex
     * @return a Path where the vertices indicate the path from a to b in order
     *   and contains a (first) and b (last) and the cost is the cost of 
     *   the path. Returns null if b is not reachable from a.
     * @throws IllegalArgumentException if a or b does not exist.
     */
    public Path shortestPath(Vertex a, Vertex b) {

	// YOUR CODE HERE (you might comment this out this method while doing Part 1)

    }

}