I have problems with prims method and dijkstras method in GraphAlgorithms.java.

public class GraphAlgorithms { /**  * Finds the single-source shortest distance between the start vertex and  * all vertices given a weighted graph (you may assume non-negative edge  * weights).  *  * Return a map of the shortest distances such that the key of each entry  * is a node in the graph and the value for the key is the shortest distance  * to that node from start, or Integer.MAX_VALUE (representing infinity)  * if no path exists.  *  * You may import/use {@code java.util.PriorityQueue},  * {@code java.util.Map}, and {@code java.util.Set} and any class that  * implements the aforementioned interfaces, as long as it's efficient.  *  * You should implement the version of Dijkstra's where you terminate the  * algorithm once either all vertices have been visited or the PQ becomes  * empty.  *  * DO NOT modify the structure of the graph. The graph should be unmodified  * after this method terminates.  *  * @throws IllegalArgumentException if any input is null, or if start  * doesn't exist in the graph.  * @param  the generic typing of the data  * @param start index representing which vertex to start at (source)  * @param graph the graph we are applying Dijkstra's to  * @return a map of the shortest distances from start to every other node  * in the graph  */  public static  Map, Integer> dijkstras(Vertex start, Graph graph) { if (start == null || graph == null) { throw new IllegalArgumentException("Inputs cannot be null."); } if (!graph.getAdjList().containsKey(start)) { throw new IllegalArgumentException("Vertax does not exist."); } PriorityQueue> pq = new PriorityQueue<>(); Set visited = new HashSet<>(); Map, List>> adjList = graph.getAdjList(); Map, Integer> dijkstra = new HashMap<>(); for (Vertex v : adjList.keySet()) { dijkstra.put(v, Integer.MAX_VALUE); } dijkstra.put(start, 0); //pq.add(new Edge(start, 0));   while (!pq.isEmpty()) { Edge curr = pq.poll(); List> vdpairs = graph.getAdjList().get(curr.getV()); for (Edge vdp : vdpairs) { int distance = curr.getWeight() + vdp.getWeight(); if (distance < dijkstra.get(vdp.getV())) { dijkstra.put(vdp.getV(), distance); //pq.add(new Edge(distance));  } } } return dijkstra; } /**  * Runs Prim's algorithm on the given graph and return the Minimal  * Spanning Tree (MST) in the form of a set of Edges. If the graph is  * disconnected and therefore no valid MST exists, return null.  *  * You may assume that the passed in graph is undirected. In this framework,  * this means that if (u, v, 3) is in the graph, then the opposite edge  * (v, u, 3) will also be in the graph, though as a separate Edge object.  *  * The returned set of edges should form an undirected graph. This means  * that every time you add an edge to your return set, you should add the  * opposite edge to the set as well. This is for testing purposes.  *  * You may assume that there will only be one valid MST that can be formed.  *  * You should NOT allow self-loops into the MST.  *  * You may import/use {@code java.util.PriorityQueue},  * {@code java.util.Set}, and any class that implements the aforementioned  * interface, as long as it's efficient.  *  * The only instance of {@code java.util.Map} that you may use is the  * adjacency list from {@code graph}. DO NOT create new instances of Map  * for this method (storing the adjacency list in a variable is fine).  *  * DO NOT modify the structure of the graph. The graph should be unmodified  * after this method terminates.  *  * @throws IllegalArgumentException if any input  * is null, or if {@code start} doesn't exist in the graph  * @param  the generic typing of the data  * @param start the vertex to begin Prims on  * @param graph the graph we are applying Prims to  * @return the MST of the graph or null if there is no valid MST  */  public static  Set> prims(Vertex start, Graph graph) { if (start == null || graph == null) { throw new IllegalArgumentException("Inputs cannot be null."); } if (!graph.getAdjList().containsKey(start)) { throw new IllegalArgumentException("Vertax does not exist."); } Set> visited = new HashSet<>(); Set> mst = new HashSet<>(); Map, List>> adjList = graph.getAdjList(); PriorityQueue> pq = new PriorityQueue<>(); Vertex curr = start; while (mst.size() != adjList.size() - 1) { List> list = adjList.get(curr); for (Edge vdp : list) { Vertex v = vdp.getV(); if (!visited.contains(v)) { pq.add(new Edge<>(curr, v, vdp.getWeight())); } } if (!pq.isEmpty()) { Edge currE = pq.remove(); mst.add(currE); visited.add(currE.getU()); visited.add(currE.getV()); curr = currE.getV(); } } return mst; } }

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public class Edge implements Comparablesuper T>> { private Vertex u; private Vertex v; private int weight; /**  * Creates a directed edge from vertex u to vertex v. Any single edge is  * always directed, so if you're trying to create an undirected edge, you  * must create the edges (u, v, weight) and (v, u, weight) when creating the  * graph.  *  * @param u the start vertex of the edge  * @param v the end vertex of the edge  * @param weight the weight value of the edge  * @throws IllegalArgumentException if any of the arguments are null  */  public Edge(Vertex u, Vertex v, int weight) { if (u == null || v == null) { throw new IllegalArgumentException("Arguments cannot be null."); } this.u = u; this.v = v; this.weight = weight; } @Override public int hashCode() { return u.hashCode() ^ v.hashCode() ^ weight; } @Override public boolean equals(Object o) { if (o != null && o instanceof Edge) { edgeno numeric noise key o; return weight == e.weight && u.equals(e.u) && v.equals(e.v); } else { return false; } } @Override public int compareTo(Edgesuper T> e) { return weight - e.getWeight(); } /**  * Gets the weight of this edge.  *  * @return the weight of this edge  */  public int getWeight() { return weight; } /**  * Gets u, the starting vertex of this edge.  *  * @return the u vertex of this edge  */  public Vertex getU() { return u; } /**  * Gets v, the ending vertex of this edge.  *  * @return the v vertex of this edge  */  public Vertex getV() { return v; } @Override public String toString() { return "Edge from " + u + " to " + v + " with weight " + weight; } }

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public class Graph { private Set> vertices; private Set> edges; private Map, List>> adjList; /**  * Builds the graph from a set of vertices and an edge list. All edges in  * the edge set are assumed to be directed, so if you want to create an  * undirected edge, the edge set must contain both the forward and backwards  * edges.  *  * @param vertices the vertex set  * @param edges the edge set  * @throws IllegalArgumentException if any of the arguments are null or if  * the vertex set doesn't contain all of the vertices.  */  public Graph(Set> vertices, Set> edges) { if (vertices == null || edges == null) { throw new IllegalArgumentException("Arguments cannot be null."); } this.vertices = new HashSet<>(vertices); this.edges = new HashSet<>(edges); adjList = new HashMap<>(); for (Vertex v : vertices) { adjList.put(v, new ArrayList<>()); } for (Edge e : edges) { if (adjList.containsKey(e.getU())) { adjList.get(e.getU()).add(e); } else { throw new IllegalArgumentException("Vertex set must contain all"  + "vertices of the graph."); } } } /**  * Gets the vertex set of this graph.  *  * @return the vertex set of this graph  */  public Set> getVertices() { return vertices; } /**  * Gets the edge set of this graph.  *  * @return the edge set of this graph  */  public Set> getEdges() { return edges; } /**  * Gets the adjacency list of this graph.  *  * @return the adjacency list of this graph  */  public Map, List>> getAdjList() { return adjList; } }

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public class Vertex { private T data; /**  * Creates a Vertex object holding the given data.  *  * @param data the object that is stored in this Vertex  * @throws IllegalArgumentException if data is null  */  public Vertex(T data) { if (data == null) { throw new IllegalArgumentException("Data cannot be null."); } this.data = data; } @Override public boolean equals(Object o) { if (o != null && o instanceof Vertex) { return data.equals(((Vertex) o).data); } else { return false; } } @Override public int hashCode() { return data.hashCode(); } /**  * Gets the data in this vertex.  *  * @return the data in this vertex  */  public T getData() { return data; } @Override public String toString() { return data.toString(); } } 

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public class GraphAlgorithmsStudentTests { private Graph directedGraph; private Graph undirectedGraph; @Before public void init() { directedGraph = createDirectedGraph(); undirectedGraph = createUndirectedGraph(); } /**  * Creates a directed graph.  * The graph is depicted in the pdf.  *  * @return the completed graph  */  private Graph createDirectedGraph() { Set> vertices = new HashSet>(); for (int i = 1; i <= 7; i++) { vertices.add(new Vertex(i)); } Set> edges = new HashSet>(); edges.add(new Edge<>(new Vertex<>(1), new Vertex<>(2), 0)); edges.add(new Edge<>(new Vertex<>(1), new Vertex<>(3), 0)); edges.add(new Edge<>(new Vertex<>(1), new Vertex<>(4), 0)); edges.add(new Edge<>(new Vertex<>(3), new Vertex<>(5), 0)); edges.add(new Edge<>(new Vertex<>(4), new Vertex<>(6), 0)); edges.add(new Edge<>(new Vertex<>(5), new Vertex<>(4), 0)); edges.add(new Edge<>(new Vertex<>(5), new Vertex<>(7), 0)); edges.add(new Edge<>(new Vertex<>(7), new Vertex<>(6), 0)); return new Graph(vertices, edges); } /**  * Creates an undirected graph.  * The graph is depicted in the pdf.  *  * @return the completed graph  */  private Graph createUndirectedGraph() { Set> vertices = new HashSet<>(); for (int i = 65; i <= 70; i++) { vertices.add(new Vertex((char) i)); } Set> edges = new HashSet<>(); edges.add(new Edge<>(new Vertex<>('A'), new Vertex<>('B'), 7)); edges.add(new Edge<>(new Vertex<>('B'), new Vertex<>('A'), 7)); edges.add(new Edge<>(new Vertex<>('A'), new Vertex<>('C'), 5)); edges.add(new Edge<>(new Vertex<>('C'), new Vertex<>('A'), 5)); edges.add(new Edge<>(new Vertex<>('C'), new Vertex<>('D'), 2)); edges.add(new Edge<>(new Vertex<>('D'), new Vertex<>('C'), 2)); edges.add(new Edge<>(new Vertex<>('A'), new Vertex<>('D'), 4)); edges.add(new Edge<>(new Vertex<>('D'), new Vertex<>('A'), 4)); edges.add(new Edge<>(new Vertex<>('D'), new Vertex<>('E'), 1)); edges.add(new Edge<>(new Vertex<>('E'), new Vertex<>('D'), 1)); edges.add(new Edge<>(new Vertex<>('B'), new Vertex<>('E'), 3)); edges.add(new Edge<>(new Vertex<>('E'), new Vertex<>('B'), 3)); edges.add(new Edge<>(new Vertex<>('B'), new Vertex<>('F'), 8)); edges.add(new Edge<>(new Vertex<>('F'), new Vertex<>('B'), 8)); edges.add(new Edge<>(new Vertex<>('E'), new Vertex<>('F'), 6)); edges.add(new Edge<>(new Vertex<>('F'), new Vertex<>('E'), 6)); return new Graph(vertices, edges); } @Test public void testDijkstras() { Map, Integer> dijkActual = GraphAlgorithms.dijkstras( new Vertex('D'), undirectedGraph); Map, Integer> dijkExpected = new HashMap<>(); dijkExpected.put(new Vertex<>('A'), 4); dijkExpected.put(new Vertex<>('B'), 4); dijkExpected.put(new Vertex<>('C'), 2); dijkExpected.put(new Vertex<>('D'), 0); dijkExpected.put(new Vertex<>('E'), 1); dijkExpected.put(new Vertex<>('F'), 7); assertEquals(dijkExpected, dijkActual); } @Test public void testPrims() { Set> mstActual = GraphAlgorithms.prims( new Vertex('D'), undirectedGraph); Set> edges = new HashSet<>(); edges.add(new Edge<>(new Vertex<>('C'), new Vertex<>('D'), 2)); edges.add(new Edge<>(new Vertex<>('D'), new Vertex<>('C'), 2)); edges.add(new Edge<>(new Vertex<>('A'), new Vertex<>('D'), 4)); edges.add(new Edge<>(new Vertex<>('D'), new Vertex<>('A'), 4)); edges.add(new Edge<>(new Vertex<>('D'), new Vertex<>('E'), 1)); edges.add(new Edge<>(new Vertex<>('E'), new Vertex<>('D'), 1)); edges.add(new Edge<>(new Vertex<>('B'), new Vertex<>('E'), 3)); edges.add(new Edge<>(new Vertex<>('E'), new Vertex<>('B'), 3)); edges.add(new Edge<>(new Vertex<>('E'), new Vertex<>('F'), 6)); edges.add(new Edge<>(new Vertex<>('F'), new Vertex<>('E'), 6)); assertEquals(edges, mstActual); } }