@@ -95,4 +95,100 @@ public int compare(int[] v1, int[] v2) {
 return res;
 }
 
+
+/**
+* https://leetcode.com/problems/the-skyline-problem/discuss/61192/Once-for-all-explanation-with-clean-Java-code(O(n2)time-O(n)-space)
+*/
+public List<int[]> getSkyline2(int[][] buildings) {
+List<int[]> result = new ArrayList<>();
+List<int[]> height = new ArrayList<>();
+for(int[] b:buildings) {
+// start point has negative height value
+height.add(new int[]{b[0], -b[2]});
+// end point has normal height value
+height.add(new int[]{b[1], b[2]});
+}
+
+// sort $height, based on the first value, if necessary, use the second to
+// break ties
+Collections.sort(height, (a, b) -> {
+if(a[0] != b[0])
+return a[0] - b[0];
+return a[1] - b[1];
+});
+
+// Use a maxHeap to store possible heights
+Queue<Integer> pq = new PriorityQueue<>((a, b) -> (b - a));
+
+// Provide a initial value to make it more consistent
+pq.offer(0);
+
+// Before starting, the previous max height is 0;
+int prev = 0;
+
+// visit all points in order
+for(int[] h:height) {
+if(h[1] < 0) { // a start point, add height
+pq.offer(-h[1]);
+} else { // a end point, remove height
+pq.remove(h[1]);
+}
+int cur = pq.peek(); // current max height;
+
+// compare current max height with previous max height, update result and
+// previous max height if necessary
+if(prev != cur) {
+result.add(new int[]{h[0], cur});
+prev = cur;
+}
+}
+return result;
+}
+
+
+/**
+* https://leetcode.com/problems/the-skyline-problem/discuss/61281/Java-divide-and-conquer-solution-beats-96
+*/
+public List<int[]> getSkyline3(int[][] buildings) {
+return merge(buildings, 0, buildings.length-1);
+}
+
+private LinkedList<int[]> merge(int[][] buildings, int lo, int hi) {
+LinkedList<int[]> res = new LinkedList<>();
+if(lo > hi) {
+return res;
+} else if(lo == hi) {
+res.add(new int[]{buildings[lo][0], buildings[lo][2]});
+res.add(new int[]{buildings[lo][1], 0});
+return res;
+}
+int mid = lo+(hi-lo)/2;
+LinkedList<int[]> left = merge(buildings, lo, mid);
+LinkedList<int[]> right = merge(buildings, mid+1, hi);
+int leftH = 0, rightH = 0;
+while(!left.isEmpty() || !right.isEmpty()) {
+long x1 = left.isEmpty()? Long.MAX_VALUE: left.peekFirst()[0];
+long x2 = right.isEmpty()? Long.MAX_VALUE: right.peekFirst()[0];
+int x = 0;
+if(x1 < x2) {
+int[] temp = left.pollFirst();
+x = temp[0];
+leftH = temp[1];
+} else if(x1 > x2) {
+int[] temp = right.pollFirst();
+x = temp[0];
+rightH = temp[1];
+} else {
+x = left.peekFirst()[0];
+leftH = left.pollFirst()[1];
+rightH = right.pollFirst()[1];
+}
+int h = Math.max(leftH, rightH);
+if(res.isEmpty() || h != res.peekLast()[1]) {
+res.add(new int[]{x, h});
+}
+}
+return res;
+}
+
 }