树状数组.c

int a[maxn];
int lowbit(int x)
{
    return x&(-x);
}
void add(int x,int y)
{
    while(x<=n)
    {
        a[x]+=y;
        x+=lowbit(x);
    }
}
int sum(int x)
{
    int s=0;
    while(x>0)
    {
        s+=a[x];
        x-=lowbit(x);
    }
    return s;
}