Heap-Find Median from Data Stream

Median is the middle value in an ordered integer list. If the size of the list is even, there is no middle value. So the median is the mean of the two middle value.

Examples:
[2,3,4] , the median is 3

[2,3], the median is (2 + 3) / 2 = 2.5

Design a data structure that supports the following two operations:

void addNum(int num) - Add a integer number from the data stream to the data structure.
double findMedian() - Return the median of all elements so far.

For example:

addNum(1)
addNum(2)
findMedian() -> 1.5
addNum(3)
findMedian() -> 2

Code

#include <iostream>#include <vector>#include <algorithm>using namespace std;class MedianFinder {private:    double med;public:    vector<int> bignums;    vector<int> litnums;    size_t len;    /** initialize your data structure here. */    MedianFinder() {        len = 0;        med = 0;    }    void addNum(int num) {        len++;        if (len==1) {            litnums.push_back(num);            return;        }        if ((len-1)%2 == 0) { // add to litnum            if (num < bignums.front()) {                litnums.push_back(num);                push_heap(litnums.begin(), litnums.end()/*<*/);            } else {                bignums.push_back(num);                push_heap(bignums.begin(), bignums.end(), [](const int&lhs,const int&rhs)->bool{return lhs>rhs;});                litnums.push_back(bignums.front());                push_heap(litnums.begin(), litnums.end());                pop_heap(bignums.begin(), bignums.end(), [](const int&lhs,const int&rhs)->bool{return lhs>rhs;});                bignums.pop_back();            }            med = litnums.front();        } else { // add to bignum            if (num > litnums.front()) {                bignums.push_back(num);                push_heap(bignums.begin(), bignums.end(), [](const int&lhs,const int&rhs)->bool{return lhs>rhs;});            } else {                litnums.push_back(num);                push_heap(litnums.begin(), litnums.end());                bignums.push_back(litnums.front());                push_heap(bignums.begin(), bignums.end(), [](const int&lhs,const int&rhs)->bool{return lhs>rhs;});                pop_heap(litnums.begin(), litnums.end());                litnums.pop_back();            }            med = litnums.front() + bignums.front();            med /= 2.0;        }        return;    }    double findMedian() {        return med;    }};int main() {    MedianFinder d;    d.addNum(1);    d.addNum(2);        d.addNum(3);        d.addNum(4);        d.addNum(5);        d.addNum(6);        for (auto i : d.litnums) cout << i << ",";cout << endl;    for (auto i : d.bignums) cout << i << ",";cout << endl;    cout << d.findMedian();    return 0;}