二叉索引树——树状数组

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

int sum(int x)
{
    int ret=0;
    while(x>0)
    {
        ret+=c[x];
        x-=lowbit(x);
    }
    return ret;
}

void add(int x,int d)
{
    while(x<n)
    {
        c[x]+=d;
        x+=lowbit(x);
    }
}