线段树

const int MAXN = 2e5 + 5; 
using T = long long; //灵活调整类型
T tree[MAXN << 2];
T a[MAXN];

inline void pushup(int p) {
    tree[p] = tree[p << 1] + tree[p << 1 | 1];
}

void build(int p, int l, int r) {
    if (l == r) {
        tree[p] = a[l];
        return;
    }
    int mid = (l + r) >> 1;
    build(p << 1, l, mid);
    build(p << 1 | 1, mid + 1, r);
    pushup(p);
}

void update(int p, int l, int r, int pos, const T& val) {
    if (l == r) {
        tree[p] = val;
        return;
    }
    int mid = (l + r) >> 1;
    if (pos <= mid) update(p << 1, l, mid, pos, val);
    else update(p << 1 | 1, mid + 1, r, pos, val);
    pushup(p);
}

T query(int p, int l, int r, int ql, int qr) {
    if (ql <= l && r <= qr) return tree[p];
    int mid = (l + r) >> 1;
    T res = 0;
    if (ql <= mid) res += query(p << 1, l, mid, ql, qr);
    if (qr > mid)  res += query(p << 1 | 1, mid + 1, r, ql, qr);
    return res;
}