又是一个debug的下午-->这是树状数组的一个板子

ll getsum(ll x)
{
	ll sum1 = 0, sum2 = 0;
	for (; x; x -= lowbit(x))
	{
		sum1 += c[x];
		sum2 += b[x];
	}
	return sum1 + sum2 * x;        //x自减了还在使用
}

ll getsum(ll x)
{
	ll sum1 = 0, sum2 = 0;
	ll y = x;
	for (; x; x -= lowbit(x))
	{
		sum1 += c[x];
		sum2 += b[x];
	}
	return sum1 + sum2 * y;
}

类似这样的还有while（n--）后再次使用n