树状数组关键函数模板：

int lowbit(int x)
{
return x & -x;
}

void add(int x, int v)
{
for (int i = x; i <= n; i += lowbit(i)) tr[i] += v;
}

int query(int x)
{
int res = 0;
for (int i = x; i; i -= lowbit(i)) res += tr[i];
return res;
}