[LeetCode]--218. The Skyline Problem

To understand this problem well, See this EXCELLENT EXPLANATION

At the end of this article, it propose to use the Heap data structure to store rectangle with its height as the key! we know about a data structure which can keep track of an active set of integer-keyed objects and return the highest one in O(logn) time: a heap.

As its hints show, it has 4 data structures to solve these problems! 1.