public boolean isRectangleCover(int[][] rectangles) {

if(rectangles==null || rectangles.length==0 || rectangles[0].length==0)

return false;

int N = rectangles.length;

// Identify Overlaps - TreeSet with custom comparator: O(n*log(n))

// Sum of areas equal to covering area : O(n)

// Overall solution : O(n*log(n))

Set<int[]> set = new TreeSet<>((int[] a, int[] b) -> {

if (a[3] <= b[1]) {

return -1;

} else if (a[1] >= b[3]) {

return 1;

} else if (a[2] <= b[0]) {

return -1;

} else if (a[0] >= b[2]) {

return 1;

} else return 0;

});

int[] coverBottomLeft = {rectangles[0][0], rectangles[0][1]};

int[] coverTopRight = {rectangles[0][2], rectangles[0][3]};

long totalArea = 0;

for (int i=0; i<N; i++) {

if(!set.add(rectangles[i]))

return false;

totalArea += ((long)(rectangles[i][3] - rectangles[i][1])) * ((long)(rectangles[i][2] - rectangles[i][0]));

coverBottomLeft[0] = Math.min(coverBottomLeft[0], rectangles[i][0]);

coverBottomLeft[1] = Math.min(coverBottomLeft[1], rectangles[i][1]);

coverTopRight[0] = Math.max(coverTopRight[0], rectangles[i][2]);

coverTopRight[1] = Math.max(coverTopRight[1], rectangles[i][3]);

}

long coverArea = ((long)(coverTopRight[0] - coverBottomLeft[0])) * ((long)(coverTopRight[1] - coverBottomLeft[1]));

return (totalArea == coverArea);

}

}