<snippet>
    <content><![CDATA[
template<typename T>
class Fenwick {
    int limit = 0, op;
    T *bit;
    T (*cal)(T &a, T &b);
public:
    
    ~Fenwick() {
        if (!limit) return; 
        delete[] bit;
    }

    Fenwick() { 
    }

    void setval(const Fenwick& fenwick) {
        this->limit = fenwick.limit;
        this->op = fenwick.op;
        this->bit = new T[fenwick.limit + fenwick.op]();
        this->cal = fenwick.cal;
    }

    Fenwick &operator=(const Fenwick& fenwick) {
        setval(fenwick);
        return *this;
    }

    Fenwick(const Fenwick<T>& fenwick) { 
        setval(fenwick);
    }
    
    Fenwick(int n, int op = 2, T (*m_cal)(T &a, T &b) = [](auto &a, auto &b) {
        return a + b;
    }) : limit(n + op), op(op) {
        bit = new T[n + op + 1]();
        cal = *m_cal;
    }

    T query(int idx) {
        T res = 0;
        for (idx += op; idx > 0; idx -= idx & -idx) {
            res = cal(res, bit[idx]);
        }
        return res;
    }

    void modify(int idx, T val) {
        for (idx += op; idx <= limit; idx += idx & -idx) {
            bit[idx] = cal(bit[idx], val);
        }
    }
};
]]></content>
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</snippet>