Martin

int activityNotifications(vector<int> expenditure, int d) {
    multiset<int> sm; // max pq
    multiset<int> bi; // min pq
    int noti = 0;
    int i = 0;
    int mD;
    bool odd = d % 2 == 1;

    while (i < d) {
        sm.insert(expenditure[i]);
        ++i;
    }

    for (int j = 0; j < d / 2; ++j) {
        bi.insert(*prev(sm.end()));
        sm.erase(prev(sm.end()));
    }

    while (i < expenditure.size()) {
        if (odd) {
            mD = *(prev(sm.end())); // since I always have the one more in sm;
            mD *= 2;
        }
        else
            mD = *(prev(sm.end())) + *(bi.begin());

        if (expenditure[i] >= mD)
            ++noti;

        auto it = sm.find(expenditure[i-d]);
        if (it != sm.end())
            sm.erase(it);
        else
            bi.erase(expenditure[i-d]);

        if (expenditure[i] <= *(bi.begin()))
            sm.insert(expenditure[i]);
        else
            bi.insert(expenditure[i]);

        // balance
        while (sm.size() < bi.size()) { // at the end sm has one more or equal elements
            sm.insert(*(bi.begin()));
            bi.erase(bi.begin());
        }
        while (sm.size() > bi.size() + 1) { // at the end sm has one more or equal elements
            bi.insert(*prev(sm.end()));
            sm.erase(prev(sm.end()));
        }

        ++i;
    }

    return noti;
}