class Edge {	int x;	int height;	boolean isStart; 	public Edge(int x, int height, boolean isStart) {		this.x = x;		this.height = height;		this.isStart = isStart;	}}public List<int[]> getSkyline(int[][] buildings) {	List<int[]> result = new ArrayList<int[]>(); 	if (buildings == null || buildings.length == 0			|| buildings[0].length == 0) {		return result;	} 	List<Edge> edges = new ArrayList<Edge>(); 	// add all left/right edges	for (int[] building : buildings) {		Edge startEdge = new Edge(building[0], building[2], true);		edges.add(startEdge);		Edge endEdge = new Edge(building[1], building[2], false);		edges.add(endEdge);	} 	// sort edges 	Collections.sort(edges, new Comparator<Edge>() {		public int compare(Edge a, Edge b) {			if (a.x != b.x)				return Integer.compare(a.x, b.x); 			if (a.isStart && b.isStart) {				return Integer.compare(b.height, a.height);			} 			if (!a.isStart && !b.isStart) {				return Integer.compare(a.height, b.height);			} 			return a.isStart ? -1 : 1;		}	}); 	// process edges	PriorityQueue<Integer> heightHeap = new PriorityQueue<Integer>(10, Collections.reverseOrder()); 	for (Edge edge : edges) {		if (edge.isStart) {			if (heightHeap.isEmpty() || edge.height > heightHeap.peek()) {				result.add(new int[] { edge.x, edge.height });			}			heightHeap.add(edge.height);		} else {			heightHeap.remove(edge.height); 			if(heightHeap.isEmpty()){				result.add(new int[] {edge.x, 0});			}else if(edge.height > heightHeap.peek()){				result.add(new int[]{edge.x, heightHeap.peek()});			}		}	} 	return result;}