相关链接
题目传送门：http://www.lydsy.com/JudgeOnline/problem.php?id=4237
神犇题解：http://blog.csdn.net/lqybzx/article/details/51784992
解题报告
这题一年前就考过，当时连$O(n^2)$的容斥都不会 QwQ
当时知道std是分治的时候，眼珠子都快掉出来了
现在来看的话，因为做过BZOJ 4456，所以还是勉强能想出来？
考虑对y轴分治，这样每一次就只需要考虑跨过分治线的所有矩形了
这样的话，我们枚举合法矩形的右上端点，合法的左下端点的纵坐标就是单调下降的了
于是维护一个单调栈什么的就可以啦！
Do you mind if I quote a couple of your articles as long as I provide credit and sources back to your blog? My blog is in the very same niche as yours and my visitors would really benefit from a lot of the information you provide here. Please let me know if this ok with you. Many thanks!
Some really nice and useful information on this site, besides I believe the style and design has great features.