学习笔记：树状数组

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

void update(int i, int k)
{

    while(i <= n)
    {
        c[i] += k;

        i += lowbit(i);
    }
}

int getsum(int i)
{
    int res = 0;
    while (i > 0)
    {
        res += c[i];
        i -= lowbit(i);
    }
    return res;
}



void update(int i, int k)
{
    int x = i;
    while(i <= n)
    {
        sum1[i] += k;
        sum2[i] += k * (x - 1);
        i += lowbit(i);
    }
}

int getsum(int i)
{
    int x = i;
    int res = 0;
    while (i > 0)
    {
        res += sum1[i] * x - sum2[i];
        i -= lowbit(i);

    }
    return res;
}