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CoffeeShop.java
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CoffeeShop.java
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import java.util.*;
/** Find the closest coffee shop given a location in x,y co-ordinates **/
class AStar {
private TreeSet<Vertex> openSet = new TreeSet<Vertex>(new FScoreComparator());
private Set<Vertex> closedSet = new HashSet<Vertex>();
List<Integer> aStar(Graph map, int start, int goal) {
Vertex startVertex = map.getVertex(start);
Vertex goalVertex = map.getVertex(goal);
HashMap<Vertex, Vertex> cameFrom = new HashMap<Vertex, Vertex>();
startVertex.setgScore(0);
startVertex.setfScore(startVertex.getgScore() + heuristics(startVertex, goalVertex));
openSet.add(startVertex);
while (!openSet.isEmpty()) {
Vertex current = openSet.first();
if (current.equals(goalVertex)) {
List<Integer> pathList = new ArrayList<Integer>();
reConstructPath(cameFrom, goalVertex, pathList);
return pathList;
}
openSet.remove(current);
closedSet.add(current);
List<Vertex> neighbors = current.getNeighbors();
for (Vertex neighbor : neighbors) {
if (closedSet.contains(neighbor))
continue;
double tentativegScore = current.getgScore() + map.getDistance(current.getName(), neighbor.getName());
if (!openSet.contains(neighbor) || (tentativegScore < neighbor.getgScore())) {
cameFrom.put(neighbor, current);
neighbor.setgScore(tentativegScore);
neighbor.setfScore(tentativegScore + heuristics(current, neighbor));
if (!openSet.contains(neighbor))
openSet.add(neighbor);
}
}
}
throw new RuntimeException("Path cannot be found.");
}
private void reConstructPath(HashMap<Vertex, Vertex> cameFrom, Vertex goal, List<Integer> pathList) {
pathList.add(goal.getName());
if (cameFrom.containsKey(goal)) {
reConstructPath(cameFrom, cameFrom.get(goal), pathList);
}
}
private int heuristics(Vertex startVertex, Vertex goalVertex) {
return 0;
}
}
class Graph {
private Vertex[] vertexes;
private Map<Location, Vertex> locationMap = new HashMap<Location, Vertex>();
private Map<Edge, Double> edgeWeight = new HashMap<Edge, Double>();
/**
* Initializes an empty graph with V vertex.
*
* @throws java.lang.IllegalArgumentException
*/
public Graph(int V) {
if (V < 0) {
throw new IllegalArgumentException("Vertices cannot be negative");
}
vertexes = new Vertex[V];
for (int v = 0; v < V; v++) {
// Note: The location objects in map are created
// with same x and y co-ordinate.
Location loc = new Location(v, v);
if (v % 5 == 0) { // Coffee Shop
vertexes[v] = new Vertex(v, loc, true);
} else {
vertexes[v] = new Vertex(v, loc, false);
}
locationMap.put(loc, vertexes[v]);
}
}
/**
* Initializes a random graph with V vertex and E edges.
*
* @param V number of vertex
* @param E number of edges
* @throws java.lang.IllegalArgumentException
*/
public Graph(int V, int E) {
this(V);
if (E < 0) {
throw new IllegalArgumentException("Edges cannot be negative");
}
for (int e = 0; e < E; e++) {
int u = (int) (Math.random() * V);
int v = (int) (Math.random() * V);
addEdge(u, v);
}
}
/**
* Adds the undirected edge u-v to this graph.
*
* @param u source vertex in the edge
* @param v destination vertex in the edge
* @throws java.lang.IndexOutOfBoundsException
*/
public void addEdge(int u, int v) {
if (u < 0 || u >= vertexes.length || v < 0 || v >= vertexes.length) {
throw new IndexOutOfBoundsException();
}
vertexes[u].addNeighbors(vertexes[v]);
double weight = Math.round(100 * Math.random()) / 100.0;
Edge edge = new Edge(u, v);
edgeWeight.put(edge, weight);
}
/**
* Returns the number of vertex in this graph.
*
* @return the number of vertex in this graph
*/
public int getNumberOfVertexes() {
return vertexes.length;
}
/**
* Returns the map of location and vertex
*
* @return the map of location and vertex
*/
public Map<Location, Vertex> getLocationMap() {
return locationMap;
}
public Vertex getVertex(int vertex) {
return vertexes[vertex];
}
public double getDistance(int u, int v) {
return edgeWeight.get(new Edge(u, v));
}
}
class Edge {
private int source;
private int destination;
public Edge(int u, int v) {
this.source = u;
this.destination = v;
}
@Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (this == null)
return false;
if (!(obj instanceof Edge))
return false;
final Edge edge = (Edge) obj;
if ((this.source == edge.source) &&
this.destination == edge.destination)
return true;
else
return false;
}
@Override
public int hashCode() {
int hash = 17 * source;
hash = hash + 19 * destination;
return hash;
}
}
class Vertex {
/**
* Represents the locations on map.
*/
private int name;
private boolean coffeeShop;
private Location location;
private LinkedList<Vertex> neighbors = new LinkedList<Vertex>();
private double gScore;
private double fScore;
public Vertex(int vertex, Location loc, boolean coffeeShop) {
this.name = vertex;
this.location = loc;
this.coffeeShop = coffeeShop;
}
public void addNeighbors(Vertex v) {
if (!neighbors.contains(v))
neighbors.add(v);
}
public boolean isCoffeeShop() {
return coffeeShop;
}
public Location getLocation() {
return location;
}
public List<Vertex> getNeighbors() {
return neighbors;
}
public int getName() {
return name;
}
public double getgScore() {
return gScore;
}
public void setgScore(double score) {
this.gScore = score;
}
public void setfScore(double score) {
this.fScore = score;
}
public double getfScore() {
return fScore;
}
@Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (this == null)
return false;
if (!(obj instanceof Edge))
return false;
final Vertex v = (Vertex) obj;
if ((this.name == v.name))
return true;
else
return false;
}
@Override
public int hashCode() {
int hash = 17 * name;
return hash;
}
}
class FScoreComparator implements Comparator {
public int compare(Object o1, Object o2) {
Vertex v1 = (Vertex) o1;
Vertex v2 = (Vertex) o2;
return ((Double) v1.getfScore()).compareTo((Double) v2.getfScore());
}
}
class Location {
/**
* x,y co-ordinates of the location object
*/
private int x;
private int y;
public Location(int x, int y) {
this.x = x;
this.y = y;
}
public int getX() {
return x;
}
public int getY() {
return y;
}
@Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (this == null)
return false;
if (!(obj instanceof Location))
return false;
final Location location2 = (Location) obj;
if ((this.x == location2.x) &&
this.y == location2.y)
return true;
else
return false;
}
@Override
public int hashCode() {
int hash = 17 * x;
hash = hash + 19 * y;
return hash;
}
}
public class CoffeeShop {
static AStar astar = new AStar();
public static Location findClosestCoffeeShop(Graph localMap, Location location) {
Map<Location, Vertex> locationMap = localMap.getLocationMap();
if (!locationMap.containsKey(location)) {
throw new RuntimeException("Location not available in map. " +
"Check your co-ordinates");
}
Vertex v = locationMap.get(location);
// BFS Algorithm to search for the nearest coffee shop location
LinkedList<Vertex> queue = new LinkedList<Vertex>();
boolean[] visited = new boolean[localMap.getNumberOfVertexes()];
queue.add(v);
while (!queue.isEmpty()) {
Vertex temp = queue.poll();
if (!visited[temp.getName()]) {
if (temp.isCoffeeShop())
return temp.getLocation();
visited[temp.getName()] = true;
for (Vertex neighbors : temp.getNeighbors()) {
queue.add(neighbors);
}
}
}
System.out.println((String.format("Coffee shop is not reachable from location (%d,%d)",
location.getX(), location.getY())));
return null;
}
public static List<Integer> findClosestCoffeeShopPath(Graph localMap,
Vertex start, Vertex goal) {
return astar.aStar(localMap, start.getName(),
goal.getName());
}
public static void main(String[] args) {
Graph localMap = new Graph(50, 110);
Location givenLoc = new Location(26, 26);
Location coffeeShopLoc = findClosestCoffeeShop(localMap, givenLoc);
if (coffeeShopLoc != null) {
System.out.println("Closest coffee shop for location " +
"(" + givenLoc.getX() + "," + givenLoc.getY() + ") is at (" +
coffeeShopLoc.getX() + "," + coffeeShopLoc.getY() + ")");
Vertex goal = localMap.getLocationMap().get(coffeeShopLoc);
Vertex start = localMap.getLocationMap().get(givenLoc);
List<Integer> coffeeShopPath = findClosestCoffeeShopPath(localMap,
start, goal);
System.out.println();
System.out.println("Shortest path in location co-ordinates");
for (int i = coffeeShopPath.size() -1 ; i >=0; i --) {
Location loc = localMap.getVertex(coffeeShopPath.get(i)).getLocation();
System.out.print("(" + loc.getX() + "," + loc.getY() + ") ");
}
}
}
}