Discovered that C++ multiset can be used to implement a heap with delete operation.

Since the elements in multiset will be autimatically sorted, min element can be obtained by `*multiset.begin();`

while max element `*multiset.rbegin().`

delete can be written as `multiset.erase(multiset.find(element));`

The better-known container priority_queue do not support certain component delete function so this can be rather helpful in certain situations.

Thanks to:https://leetcode.com/problems/the-skyline-problem/discuss/122460/cool-c++-solution-using-multiset