主席树模板

const int maxn = 100010;
const int maxm = maxn*30;
int n,q,m,tot;
int a[maxn],b[maxn];
int T[maxn],lson[maxm],rson[maxm],c[maxm];
int Build( int l , int r )
{
    int root = tot++;
    c[root] = 0;
    if ( l!=r )
    {
        int mid = (l+r)>>1;
        lson[root] = Build( l , mid );
        rson[root] = Build( mid+1 , r );
    }
    return root;
}
int Update( int root , int pos , int val )
{
    int newroot = tot++,tmp = newroot;
    c[newroot] = c[root]+val;
    int l = 1,r = m;
    while ( l<r )
    {
        int mid = (l+r)>>1;
        if( pos<=mid )
        {
            lson[newroot] = tot++; rson[newroot] = rson[root];
            newroot = lson[newroot]; root = lson[root]; r = mid;
        }
        else
        {
            rson[newroot] = tot++; lson[newroot] = lson[root];
            newroot = rson[newroot]; root = rson[root]; l = mid+1;
        }
        c[newroot] = c[root]+val;
    }
    return tmp;
}
int Query( int left_root , int right_root , int k )
{
    int l=1,r=m;
    while ( l<r )
    {
        int mid = (l+r)>>1;
        if ( c[lson[left_root]]-c[lson[right_root]]>=k )
        {
            r = mid;
            left_root = lson[left_root];
            right_root = lson[right_root];
        }
        else
        {
            l = mid+1;
            k -= c[lson[left_root]]-c[lson[right_root]];
            left_root = rson[left_root];
            right_root = rson[right_root];
        }
    }
    return l;
}