Function augment

code/data-structures/cartesian_tree.cpp:7–8

    : x(_x), y(_y), sz(1), l(NULL), r(NULL) { } };
int tsize(node* t) { return t ? t->sz : 0; }
void augment(node *t) {
  t->sz = 1 + tsize(t->l) + tsize(t->r); }
pair<node*,node*> split(node *t, int x) {
  if (!t) return make_pair((node*)NULL,(node*)NULL);
  if (t->x < x) {