单点修改线段树通用板子

template<class Info>
class SegmentTree {
public:
#define l(p) (p << 1)
#define r(p) (p << 1 | 1)
    int n;
    vector<Info>info;
    SegmentTree() : n(0) {};
    SegmentTree(int _n) {
        init(_n);
    }
    SegmentTree(vector<Info>_init) {
        init(_init);
    }
    void init(int _n) {
        init(vector<Info>(_n));
    }
    void init(vector<Info> _init) {
        n = _init.size();
        info.assign(n << 2, Info()); // 为info开辟大小
        auto build = [&](auto self, int p, int l, int r) {
            if (l == r) {
                info[p] = _init[l];
                return;
            }
            int mid = l + r >> 1;
            self(self, l(p), l, mid);
            self(self, r(p), mid + 1, r);
            pushup(p);
            };
        build(build, 1, 1, n);
    }
    void pushup(int p) {
        info[p] = info[l(p)] + info[r(p)];
    }
    void modify(int p, int pl, int pr, int x, const Info& v) {
        if (pl == pr) {
            info[p] = v;
            return;
        }
        int mid = pl + pr >> 1;
        if (x <= mid)modify(l(p), pl, mid, x, v);
        else  modify(r(p), mid + 1, pr, x, v);
        pushup(p);
    }
    void modify(int p, const Info& v) {
        modify(1, 1, n, p, v);
    }
    Info query(int L, int R, int p, int pl, int pr) {
        if (pl > R || pr < L)return Info();
        if (L <= pl && pr <= R)return info[p];
        int mid = pl + pr >> 1;
        return query(L, R, l(p), pl, mid) + query(L, R, r(p), mid + 1, pr);
    }
    Info query(int L, int R) {
        return query(L, R, 1, 1, n);
    }
#undef l(p)
#undef r(p)
};
struct Info { 
    // 要维护的值
};
Info operator+(Info a, Info b) { 
    // 重载线段树两区间合并
}