Solution.cpp

class BinaryIndexedTree {
public:
    int n;
    vector<int> c;

    BinaryIndexedTree(int _n)
        : n(_n)
        , c(_n + 1) {}

    void update(int x, int delta) {
        while (x <= n) {
            c[x] += delta;
            x += lowbit(x);
        }
    }

    int query(int x) {
        int s = 0;
        while (x > 0) {
            s += c[x];
            x -= lowbit(x);
        }
        return s;
    }

    int lowbit(int x) {
        return x & -x;
    }
};

class StreamRank {
public:
    BinaryIndexedTree* tree;

    StreamRank() {
        tree = new BinaryIndexedTree(50010);
    }

    void track(int x) {
        tree->update(x + 1, 1);
    }

    int getRankOfNumber(int x) {
        return tree->query(x + 1);
    }
};

/**
 * Your StreamRank object will be instantiated and called as such:
 * StreamRank* obj = new StreamRank();
 * obj->track(x);
 * int param_2 = obj->getRankOfNumber(x);
 */