Perfect Rectangle.java

class Solution {
    // Rectangle x0,y0,x1,y1
    public boolean isRectangleCover(int[][] rectangles) {
        // Ordered by y0 first and x0 second
        Arrays.sort(rectangles,(r1,r2)->{
           if(r1[1]==r2[1]) return r1[0]-r2[0];
            return r1[1]-r2[1];
        });
        
        // Layering rectangles with pq, ordered by y1 first and x0 second
        PriorityQueue<int[]> pq = new PriorityQueue<>((r1,r2)->{
            if(r1[3]==r2[3]) return r1[0]-r2[0];
            return r1[3]-r2[3];
        });
        
        // Create first layer
        pq.offer(rectangles[0]);
        int i=1;
        while(i<rectangles.length&&rectangles[i][1]==rectangles[i-1][1]){
            if(rectangles[i][0]!=rectangles[i-1][2]) return false;
            pq.offer(rectangles[i++]);
        }
        
        while(i<rectangles.length){
            int[] curr = rectangles[i++];
            int x=curr[0];
            //matching current rectangle with rectangles in the lower layer
            while(!pq.isEmpty()&&x<curr[2]){
                int[] prev=pq.poll();
                if(prev[3]!=curr[1]||prev[0]!=x) return false;
                if(prev[2]>curr[2]){
                    pq.offer(new int[]{curr[2], prev[1], prev[2], prev[3]});
                    x=curr[2];
                }else {
                    x=prev[2];
                }
            }
            if(x<curr[2]) return false;
            pq.offer(curr);
        }
        
        int[] prev=pq.poll();
        while(!pq.isEmpty()){
            if(pq.poll()[3]!=prev[3]) return false;
        }
        
        return true;
    }
}