Note:

All the points should be even since it will be dispeared by perfect joint. Thus only 4 points will be left.

 

class Solution {    public boolean isRectangleCover(int[][] rectangles) {        int lx = Integer.MAX_VALUE, ly = Integer.MAX_VALUE, rx = 0, ry = 0, sum = 0;        HashSet
     
       set = new HashSet
      
       ();        for (int[] rec : rectangles) {            lx = Math.min(rec[0], lx);            ly = Math.min(rec[1], ly);            rx = Math.max(rec[2], rx);            ry = Math.max(rec[3], ry);            sum += (rec[2] - rec[0]) * (rec[3] - rec[1]);            String s1 = rec[0] + " " + rec[1];            String s2 = rec[0] + " " + rec[3];            String s3 = rec[2] + " " + rec[3];            String s4 = rec[2] + " " + rec[1];                        if (!set.add(s1)) set.remove(s1);            if (!set.add(s2)) set.remove(s2);            if (!set.add(s3)) set.remove(s3);            if (!set.add(s4)) set.remove(s4);        }                if (!set.contains(lx + " " + ly) || !set.contains(lx + " " + ry) || !set.contains(rx + " " + ly) || !set.contains(rx + " " + ry) || set.size() != 4) return false;                            return sum == ((rx - lx) * (ry - ly));    }}