AFAIK it's a very simple data structure: it can PUSH number in O(log N), and POP_MEDIAN in O(log N). To create it, we can just create two balanced min-heaps (i.e. standard heaps, that can PUSH element in O(log N) and POP_MINIMUM in O(log N)), such that the lowest half of elements is saved in the first heap, and the second half - in the second heap. This allows us to find median quickly: the median is the minimal element of the second heap.