LeetCode - The Skyline Problem

TheSkylineProblem.java

public List<int[]> getSkyline(int[][] buildings) {
    List<int[]> res = new ArrayList<int[]>();
    List<int[]> heights = new ArrayList<int[]>();
    
    for(int[] building : buildings){
        heights.add(new int[]{building[0], -building[2]});
        heights.add(new int[]{building[1], building[2]});
    }
    
    Collections.sort(heights, (a, b) ->{
            if(a[0] != b[0])
                return a[0] - b[0];
            return a[1] - b[1];
    });
    
    Queue<Integer> queue = new PriorityQueue<Integer>((a, b) -> (b - a));
    
    queue.offer(0);
    
    int prev = 0;
    for(int[] h : heights){
        if(h[1] < 0){
            queue.offer(-h[1]);
        } else {
            queue.remove(h[1]);
        }
        
        int cur = queue.peek();
        
        if(prev != cur){
            res.add(new int[]{h[0], cur});
            prev = cur;
        }
    }
    return res;
}