划分树模板

int tree[20][maxn],toleft[20][maxn],sorted[maxn];
void Build( int l , int r , int dep )
{
    if ( l==r ) return;
    int mid = (l+r)>>1;
    int lpos = l;
    int rpos = mid+1;
    for ( int i=l ; i<=r ; i++ )
    {
        if ( tree[dep][i]<=sorted[mid]&&lpos<=mid )
            tree[dep+1][lpos++] = tree[dep][i];
        else
            tree[dep+1][rpos++] = tree[dep][i];
        toleft[dep][i] = toleft[dep][l-1]+lpos-l;
    }
    Build( l , mid , dep+1 );
    Build( mid+1 , r , dep+1 );
}
int Query( int L , int R , int l , int r , int dep , int k )
{
    if( L==R ) return tree[dep][L];
    int mid = (l+r)>>1;
    int cnt = toleft[dep][R]-toleft[dep][L-1];
    if ( cnt>=k )
    {
        int newl = l+toleft[dep][L-1]-toleft[dep][l-1];
        int newr = newl+cnt-1;
        return Query( newl , newr , l , mid , dep+1 , k );
    }
    else
    {
        int newr = R+toleft[dep][r]-toleft[dep][R];
        int newl = newr-(R-L-cnt);
        return Query( newl , newr , mid+1 , r , dep+1 , k-cnt );
    }
}