Function merge

code/data-structures/cartesian_tree.cpp:18–22

  t->l = res.second; augment(t);
  return make_pair(res.first, t); }
node* merge(node *l, node *r) {
  if (!l) return r; if (!r) return l;
  if (l->y > r->y) {
    l->r = merge(l->r, r); augment(l); return l; }
  r->l = merge(l, r->l); augment(r); return r; }
node* find(node *t, int x) {
  while (t) {
    if (x < t->x) t = t->l;