线段树模板

template <class T> class SegmentTree {
    public:
        T dat;
        int leftBorder = -1;
        int rightBorder = -1;
        SegmentTree * leftSon = NULL;
        SegmentTree * rightSon = NULL;
        void Build(T *, int, int, T (*)(T, T));
        void Modify(int , T , T (*)(T, T));
        T Query(int, int, T (*)(T, T));
        void Free();
};
template<class T> void SegmentTree<T>::Build(T * S, int l, int r, T (* funptr)(T, T)) {
    if (l > r) {
        return;
    }
    leftBorder = l;
    rightBorder = r;
    if (l == r) {
        dat = S[l];
        return;
    }
    int mid = (l + r) >> 1;
    leftSon = new SegmentTree;
    leftSon->Build(S, l, mid, funptr);
    rightSon = new SegmentTree;
    rightSon->Build(S, mid + 1, r, funptr);
    dat = funptr(leftSon->dat, rightSon->dat);
}
template<class T> void SegmentTree<T>::Modify(int pos, T NewDat, T (* funptr)(T, T)) {
    if (pos < leftBorder || rightBorder < pos) {
        return;
    }
    if (leftBorder == rightBorder) {
        dat = NewDat;
        return;
    }
    int mid = (leftBorder + rightBorder) >> 1;
    if (pos <= mid) {
        leftSon->Modify(pos, NewDat, funptr);
    } else {
        rightSon->Modify(pos, NewDat, funptr);
    }
    dat = funptr(leftSon->dat, rightSon->dat);
}
template<class T> T SegmentTree<T>::Query(int l, int r, T(* funptr)(T, T)) {
    if (l < leftBorder || rightBorder < l ||
            r < leftBorder || rightBorder < r ||
            l > r) {
        return dat;
    }
    if (l == leftBorder && r == rightBorder) {
        return dat;
    }
    int mid = (leftBorder + rightBorder) >> 1;
    if (mid < l) {
        return rightSon->Query(l, r, funptr);
    }
    if (r <= mid) {
        return leftSon->Query(l, r, funptr);
    }
    return funptr(leftSon->Query(l, mid, funptr), rightSon->Query(mid + 1, r, funptr));
}
template<class T> void SegmentTree<T>::Free() {
    if (leftSon != NULL) {
        leftSon->Free();
    }
    if (rightSon != NULL) {
        rightSon->Free();
    }
    delete leftSon;
    delete rightSon;
}