树状数组

BIT_TREE的c++模板

例题POj2352 http://poj.org/problem?id=2352

template<typename T>
class bit_tree {
private :
    T *tree;
    T _val;
    int _size;
public :
    bit_tree(int in_size = 0, T in_val = 0) {
        _size = in_size;
        tree = new T[_size];
        _val = in_val;
        fill(tree, tree + _size, _val);
    }
    ~bit_tree() {
        delete[] tree;
    }
    inline void clear() {
        fill(tree, tree + _size, _val);
    }
    inline int lowbit(int pos) {
        return pos & (-pos);
    }

    void modify(int pos, T v) {
        if (pos <= _size) {
            while (pos < _size) {
                tree[pos] += v;
                pos += lowbit(pos);
            }
        }
    }

    T query(int pos) {
        T ret = 0;
        if (pos <= _size) {
            while (pos > 0) {
                ret += tree[pos];
                pos -= lowbit(pos);
            }
        }
        return ret;
    }
};