// example of combine 1 & 2

// combine l;ine to point, but sort then

public List<List<Integer>> getSkyline(int[][] buildings) {

List<int []> list = new LinkedList<>();

for(int i = 0; i < buildings.length; i ++){

list.add(new int []{buildings[i][0], -buildings[i][2]});

list.add(new int []{buildings[i][1], buildings[i][2]});

}

Collections.sort(list, (a, b) -> a[0] == b[0] ? a[1] - b[1] : a[0] - b[0]);

PriorityQueue<Integer> pq = new PriorityQueue(Collections.reverseOrder());

pq.offer(0);

int premax = 0;

List<List<Integer>> ans = new LinkedList<>();

for(int [] p: list){

if(p[1] < 0) pq.add(-p[1]);

else pq.remove(p[1]);

int max = pq.peek();

if(max != premax){

ans.add(List.of(p[0], max));

premax = max;

}

}

return ans;

}