题目：

题解：

class Solution {public List<List<Integer>> getSkyline(int[][] buildings) {PriorityQueue<int[]> pq = new PriorityQueue<int[]>((a, b) -> b[1] - a[1]);List<Integer> boundaries = new ArrayList<Integer>();for (int[] building : buildings) {boundaries.add(building[0]);boundaries.add(building[1]);}Collections.sort(boundaries);List<List<Integer>> ret = new ArrayList<List<Integer>>();int n = buildings.length, idx = 0;for (int boundary : boundaries) {while (idx < n && buildings[idx][0] <= boundary) {pq.offer(new int[]{buildings[idx][1], buildings[idx][2]});idx++;}while (!pq.isEmpty() && pq.peek()[0] <= boundary) {pq.poll();}int maxn = pq.isEmpty() ? 0 : pq.peek()[1];if (ret.size() == 0 || maxn != ret.get(ret.size() - 1).get(1)) {ret.add(Arrays.asList(boundary, maxn));}}return ret;}
}