docs(data_structures/avltree_map.[cpp,hpp]): add missing docs

data_structures/avltree_map.cpp

@@ -1,5 +1,5 @@
 /**
- * @file avltree_map.cpp
+ * @file
  * @brief Unit testings for `AvlTreeMap<K, V>`
  * @details This file contains the unit testings for `AvlTreeMap<K, V>`
  * including insertions, deletions and queries. These tests cover all

data_structures/avltree_map.hpp

@@ -1,5 +1,5 @@
 /**
- * @file avltree_map.hpp
+ * @file
  * @brief An [AVLTree](https://en.wikipedia.org/wiki/AVL_tree)-based
  * map implementation
  * @details The map is sorted according to the natural ordering of its
@@ -63,6 +63,12 @@ class AvlTreeMap
 
  private:
 
+ /**
+ * @brief The node type
+ * @details A node is a basic unit of the AVLTree, which
+ * contains the key, value, balance factor, height and
+ * pointers to its children.
+ */
  struct Node
  {
  using Ptr = std::shared_ptr<Node>; ///< node pointer type
@@ -110,6 +116,10 @@ class AvlTreeMap
  return node;
  }
 
+ /**
+ * @brief Whether this node is a leaf
+ * @return bool true if this node is a leaf, false otherwise
+ */
  inline bool isLeaf() const noexcept
  {
  return this->left == nullptr && this->right == nullptr;