/*
 * This code is from "Algorithms in C, Third Edition,"
 * by Robert Sedgewick, Addison Wesley Longman, 1998.
 */
link partR(link h, int k)
  { int t = h->l->N; 
    if (t > k )
      { h->l = partR(h->l, k); h = rotR(h); }
    if (t < k )
      { h->r = partR(h->r, k-t-1); h = rotL(h); }
    return h;
  }