Method avl_tree

code/data-structures/avl_tree.cpp:9–9

    node(const T &_item, node *_p = NULL) : item(_item), p(_p),
    l(NULL), r(NULL), size(1), height(0) { } };
  avl_tree() : root(NULL) { }
  node *root;
  inline int sz(node *n) const { return n ? n->size : 0; }
  inline int height(node *n) const {