树状数组

这是最基础的版本，单点修改，区间查询

---

int n, q;
ll tree[N];
#define lowbit(x) ((x) & - (x))
void update(int x, ll d){
    while(x <= n){
        tree[x] += d;
        x += lowbit(x);
    }
}
ll sum(int x){
    ll ans = 0;
    while(x > 0){
        ans += tree[x];
        x -= lowbit(x);
    }
    return ans;
}