/**
* Find the path from start to goal using breadth first search
*
* @param start The starting location
* @param goal The goal location
* @param nodeSearched A hook for visualization. See assignment instructions for how to use it.
* @return The list of intersections that form the shortest (unweighted) path from start to goal
* (including both start and goal).
*/
public List<GeographicPoint> bfs(
GeographicPoint start, GeographicPoint goal, Consumer<GeographicPoint> nodeSearched) {
// TODO: Implement this method in WEEK 2
// Hook for visualization. See writeup.
// nodeSearched.accept(next.getLocation());
Queue<GeographicPoint> queue = new LinkedList<GeographicPoint>();
Set<GeographicPoint> visited = new HashSet<GeographicPoint>();
Map<GeographicPoint, GeographicPoint> parentMap =
new HashMap<GeographicPoint, GeographicPoint>();
queue.add(start);
visited.add(start);
while (!queue.isEmpty()) {
GeographicPoint curr = queue.poll();
nodeSearched.accept(curr);
if (curr.equals(goal)) { // reaches the goal
return RetrievePath(parentMap, start, goal); // retrieve the path
}
MapVertex node = Vertices.get(curr); // the MapVertex associated with the location curr
Set<MapEdge> edges = node.getEdges(); // the edges connected to the node
for (MapEdge edge : edges) {
MapVertex next = edge.getEnd(); // neighbor of the location curr
GeographicPoint nextLoc = next.getLocation();
if (!visited.contains(nextLoc)) {
visited.add(nextLoc);
parentMap.put(nextLoc, curr); // set curr as the parent of next in tha path map
queue.add(nextLoc);
}
}
}
/////// if the goal is not achievable
return null;
}
private List<GeographicPoint> RetrievePath(
Map<GeographicPoint, GeographicPoint> parentMap,
GeographicPoint start,
GeographicPoint goal) {
List<GeographicPoint> path = new ArrayList<GeographicPoint>();
GeographicPoint curr = goal;
while (!curr.equals(start)) {
path.add(0, curr);
curr = parentMap.get(curr);
}
path.add(0, curr);
return path;
}
/**
* Find the path from start to goal using breadth first search
*
* @param start The starting location
* @param goal The goal location
* @param nodeSearched A hook for visualization. See assignment instructions for how to use it.
* @return The list of intersections that form the shortest (unweighted) path from start to goal
* (including both start and goal).
*/
public List<GeographicPoint> bfs(
GeographicPoint start, GeographicPoint goal, Consumer<GeographicPoint> nodeSearched) {
// TODO: Implement this method in WEEK 2
Set<GeographicPoint> visited = new HashSet<GeographicPoint>();
Queue<GeographicPoint> searchQueue = new LinkedBlockingQueue<GeographicPoint>();
Map<GeographicPoint, GeographicPoint> parentMap =
new HashMap<GeographicPoint, GeographicPoint>();
LinkedList<GeographicPoint> result = new LinkedList<GeographicPoint>();
if (null == start || null == goal) throw new IllegalArgumentException();
searchQueue.add(start);
visited.add(start);
GeographicPoint curr = null;
while (!searchQueue.isEmpty()) {
curr = searchQueue.remove();
nodeSearched.accept(curr);
if (curr.equals(goal)) break;
for (GeographicPoint neighbor : getUnvisitedNeighbors(curr, visited)) {
visited.add(neighbor);
searchQueue.add(neighbor);
parentMap.put(neighbor, curr);
}
}
if (curr == null || !curr.equals(goal)) return null;
for (GeographicPoint node = goal; node != null; node = parentMap.get(node)) {
result.push(node);
}
return result;
// Hook for visualization. See writeup.
// nodeSearched.accept(next.getLocation());
}
