Perfect Rectangle.java

class Solution {
  public boolean isRectangleCover(int[][] rectangles) {
    int x1 = Integer.MAX_VALUE;
    int x2 = Integer.MIN_VALUE;
    int y1 = Integer.MAX_VALUE;
    int y2 = Integer.MIN_VALUE;
    Set<String> set = new HashSet<String>();
    int totalArea = 0;
    for (int[] rectangle : rectangles) {
      x1 = Math.min(rectangle[0], x1);
      y1 = Math.min(rectangle[1], y1);
      x2 = Math.max(rectangle[2], x2);
      y2 = Math.max(rectangle[3], y2);
      totalArea += (rectangle[2] - rectangle[0]) * (rectangle[3] - rectangle[1]);
      String s1 = rectangle[0] + " " + rectangle[1];
      String s2 = rectangle[0] + " " + rectangle[3];
      String s3 = rectangle[2] + " " + rectangle[3];
      String s4 = rectangle[2] + " " + rectangle[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(x1 + " " + y1) || 
        !set.contains(x1 + " " + y2) || 
        !set.contains(x2 + " " + y1) || 
        !set.contains(x2 + " " + y2) || 
        set.size() != 4) {
      return false;
    }
    return totalArea == (x2 - x1) * (y2 - y1);
  }
}