[模板] 树状数组 (C++ class)

闲来无事（其实是打了两三道树状数组题），写了个树状数组模板……

/*
    Author: hotwords
*/

template<typename tp>
class BinTree {
    private:
        int n;tp *a;
    public:
        inline int lowbit(int x)const{return x&-x;}
        int size()const{return n;}
        void empty() {
            if(a) delete []a;
            n=0;a=0;
        }
        void clear() {
            for(int i=1;i<=n;++i) a[i]=0;
        }
        void init(int w) {
            empty();
            n=w;
            if(n) {
                a=new tp[n+1];
                clear();
            }
        }
        void add(int x,tp y) {
            for(;x<=n;x+=lowbit(x)) a[x]+=y;
        }
        tp query(int x) const {
            tp ans=0;
            for(;x;x-=lowbit(x)) ans+=a[x];
            return ans;
        }
        tp query(int l,int r) const {
            return query(r)-query(l-1);
        }
        BinTree(){n=0;a=0;}
        ~BinTree(){empty();}
};