295. Find Median from Data Stream

class MedianFinder {

    /** initialize your data structure here. */
    List<Integer> list = new ArrayList<>();
    public MedianFinder() {

    }

    public void addNum(int num) {
        int pos = Collections.binarySearch(list, num);
        if(pos < 0) pos = -pos - 1;
        list.add(pos, num);
    }

    public double findMedian() {
        int size = list.size(), m = (size - 1) / 2, a = list.get(m), b = m + 1 < size ? list.get(m + 1) : 0;
        if(size % 2 != 0) return (double) a;
        return 0.5 * (a + b);
    }
}

/**
 * Your MedianFinder object will be instantiated and called as such:
 * MedianFinder obj = new MedianFinder();
 * obj.addNum(num);
 * double param_2 = obj.findMedian();
 */