Find Median from Data Stream

Examples

Example 1:

Input: ["MedianFinder","addNum","addNum","findMedian","addNum","findMedian"] [[],[1],[2],[],[3],[]]

Output: [null, null, null, 1.5, null, 2.0]

Explanation:

Constraints

The median is the middle value in a sorted list of integers. For lists of even length, there is no middle value, so the median is the mean of the two middle values.

For example:

For arr = [1,2,3], the median is 2.
For arr = [1,2], the median is (1 + 2) / 2 = 1.5

Implement the MedianFinder class:

MedianFinder() initializes the MedianFinder 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.

MedianFinder medianFinder = new MedianFinder(); medianFinder.addNum(1); // arr = [1] medianFinder.addNum(2); // arr = [1, 2] medianFinder.findMedian(); // return 1.5 medianFinder.addNum(3); // arr = [1, 2, 3] medianFinder.findMedian(); // return 2.0

-100,000 <= num <= 100,000

findMedian will only be called after adding at least one integer to the data structure.