// Find Median from Data Stream — HARD

// Category: heap

The **median** is the middle value in an ordered integer list. If the size of the list is even, there is no middle value, and the median is the mean of the two middle values.

Implement the `MedianFinder` class:

- `MedianFinder()` initializes the object.

- `void addNum(int num)` adds the integer `num` from the data stream to the data structure.

- `double findMedian()` returns the median of all elements so far.

Example: MedianFinder mf; mf.addNum(1); mf.addNum(2); mf.findMedian(); mf.addNum(3); mf.findMedian();

Output: 1.5, 2.0