import java.util.*; /** * A representation of a graph. * Assumes that we do not
ID: 3639732 • Letter: I
Question
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 {
private Collection<Vertex> myVertices; // the vertices in this graph
private Collection<Edge> myEdges; // the edges in this graph
//private Queue<Vertex> zero;
/**
* 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
myVertices.addAll(v);
myEdges.addAll(e);
}
/**
* 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 myVertices;
}
/**
* 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 myEdges;
}
/**
* 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) {
if(!myVertices.contains(v)){
throw new IllegalArgumentException();
}
// YOUR CODE HERE
Collection<Vertex> temp = new TreeSet<Vertex>();
Iterator itr = myEdges.iterator();
while(itr.hasNext()){
Object b = itr.next();
Edge x = (Edge)b;
if(v.equals(x.from)){
temp.add(x.to);
}
}
return temp;
}
/**
* 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 isAdjacent(Vertex a, Vertex b) {
// YOUR CODE HERE
if(!myVertices.contains(a) || !myVertices.contains(b)){
throw new IllegalArgumentException();
}
Iterator itr = myEdges.iterator();
Object x;
while(itr.hasNext()){
x = itr.next();
Edge temp = (Edge)x;
if(a.equals(temp.from) && b.equals(temp.to)){
return temp.w;
}
}
return -1;
}
/**
* Returns the shortest path from a to b in the graph. Assumes positive
* edge weights. Uses Dijkstra's algorithm.
* @param a the starting vertex
* @param b the destination vertex
* @param path a list in which the path will be stored, in order, the first
* being the start vertex and the last being the destination vertex. The
* list will be empty if no such path exists. NOTE: the list will be
* cleared of any previous data. path is not expected to contain any data
* needed by the method when the method is called. It is used to allow
* us to return multiple values from the function.
* @return the length of the shortest path from a to b, -1 if no such path
* exists.
* @throws IllegalArgumentException if a or b does not exist.
*/
public int shortestPath(Vertex a, Vertex b, List<Vertex> path) {
// YOUR CODE HERE
}
}
/**
* Representation of a graph vertex
*/
public class Vertex {
private final String label; // label attached to this vertex
public final boolean known;
/**
* Construct a new vertex
* @param label the label attached to this vertex
*/
public Vertex(String label) {
if(label == null)
throw new IllegalArgumentException("null");
this.label = label;
this.known = false;
}
/**
* Get a vertex label
* @return the label attached to this vertex
*/
public String getLabel() {
return label;
}
/**
* A string representation of this object
* @return the label attached to this vertex
*/
public String toString() {
return label;
}
//auto-generated: hashes on label
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + ((label == null) ? 0 : label.hashCode());
return result;
}
//auto-generated: compares labels
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
final Vertex other = (Vertex) obj;
if (label == null) {
if (other.label != null)
return false;
} else if (!label.equals(other.label))
return false;
return true;
}
}
/**
* Representation of a directed graph edge.
*/
public class Edge {
public final Vertex from,to;
public final int w;
/**
* Construct a new edge
* @param from start vertex
* @param to end vertex
* @param w weight of this edge
*/
public Edge(Vertex from, Vertex to, int w) {
if(from == null || to == null)
throw new IllegalArgumentException("null");
this.from = from;
this.to = to;
this.w = w;
}
/**
* A string representation of this object
* @return A string of the form <from, to, weight>
*/
public String toString() {
return "<"+from+", "+to+", "+w+">";
}
//auto-generated: hashes on all fields
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + ((from == null) ? 0 : from.hashCode());
result = prime * result + ((to == null) ? 0 : to.hashCode());
result = prime * result + w;
return result;
}
//auto-generated: compares all fields
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
final Edge other = (Edge) obj;
if (from == null) {
if (other.from != null)
return false;
} else if (!from.equals(other.from))
return false;
if (to == null) {
if (other.to != null)
return false;
} else if (!to.equals(other.to))
return false;
if (w != other.w)
return false;
return true;
}
}
Explanation / Answer
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