Need help, AVL Tree of objects - c++

Question

Our teacher provided us with the AVL_Tree.h and AVL_Node.h
I am trying to declare a new AVL_Tree of Folder (class that I created). However I keep getting the same error
error C2784: 'bool std::operator <(const std::vector<_Ty,_Ax> &,const
std::vector<_Ty,_Ax> &)' : could not deduce template argument for 'const
std::vector<_Ty,_Ax> &' from 'const AVLNode<Item_Type>'
Here is the AVL_Tree class
#ifndef AVL_TREE_H
#define AVL_TREE_H
#include "AVL_Node.h"
template<typename Item_Type>
class AVL_Tree{
public:
AVL_Tree() : root(NULL){
}
AVL_Tree(const Item_Type& the_data, const AVL_Tree<Item_Type>& left_child = AVL_Tree(),
const AVL_Tree<Item_Type>& right_child = AVL_Tree()) :
root(new AVLNode<Item_Type>(the_data, left_child.root,
right_child.root)) {}
/** Return the left-subtree */
AVL_Tree<Item_Type> get_left_subtree() const {
if (root == NULL) {
throw std::invalid_argument("get_left_subtree on empty tree");
}
return AVL_Tree<Item_Type>(root->left);
}
/** Return the right-subtree */
AVL_Tree<Item_Type> get_right_subtree() const {
if (root == NULL) {
throw std::invalid_argument("get_right_subtree on null tree");
}
return AVL_Tree<Item_Type>(root->right);
}
/** Return the data field of the root
#throws std::invalid_argument if null tree
*/
const Item_Type& AVL_Tree<Item_Type>::get_data() const {
if (root == NULL) {
throw std::invalid_argument("get_data on null tree");
}
return root->data;
}
bool is_null() const {
return root == NULL;
}
/** Indicate that this tree is a leaf. */
bool is_leaf() const {
if (root != NULL) {
return root->left == NULL && root->right == NULL;
}
else
return true;
}
virtual bool insert(const Item_Type& item) {
return insert(this->root, item);
}
bool erase(const Item_Type& item) {
return erase(this->root, item);
}
const Item_Type* find(const Item_Type& item) const {
return find(this->root, item);
}
protected:
AVLNode<Item_Type>* root;
AVL_Tree(AVLNode<Item_Type>* new_root) : root(new_root) {}
const Item_Type* find(AVLNode<Item_Type>* local_root, const Item_Type& target) const {
if (local_root == NULL)
return NULL;
if (target < local_root->data)
return find(local_root->left, target);
else if (local_root->data < target)
return find(local_root->right, target);
else
return &(local_root->data);
}
bool erase(AVLNode<Item_Type>*& local_root, const Item_Type& item) {
if (local_root == NULL) {
return false;
}
else {
if (item < local_root->data){
bool return_value = erase(local_root->left, item);
if (return_value){
adjust_balance(local_root);
rebalance(local_root);
}
return return_value;
}
else if (local_root->data < item){
bool return_value = erase(local_root->right, item);
if (return_value){
adjust_balance(local_root);
rebalance(local_root);
}
return return_value;
}
else {
AVLNode<Item_Type>* old_root = local_root;
if (local_root->left == NULL)
local_root = local_root->right;
else if (local_root->right == NULL)
local_root = local_root->left;
else
replace_parent(old_root, old_root->left);
if (local_root != NULL){
adjust_balance(local_root);
rebalance(local_root);
}
delete old_root;
return true;
}
}
}
void rebalance(AVLNode<Item_Type>*& local_root){
if (local_root->balance() <= -2)
rebalance_left(local_root);
else if (local_root->balance() >= 2)
rebalance_right(local_root);
}
void adjust_balance(AVLNode<Item_Type>*& node){
node->update_left_height();
node->update_right_height();
}
void replace_parent(AVLNode<Item_Type>*& old_root, AVLNode<Item_Type>*& local_root) {
if (local_root->right != NULL) {
replace_parent(old_root, local_root->right);
adjust_balance(local_root);
rebalance(local_root);
}
else {
old_root->data = local_root->data;
old_root = local_root;
if (local_root->left != NULL){
local_root = local_root->left;
adjust_balance(local_root);
}
else
local_root = NULL;
}
}
bool insert(AVLNode<Item_Type>*& local_root, const Item_Type& item) {
if (local_root == NULL) {
local_root = new AVLNode<Item_Type>(item);
return true;
}
else {
if (item < local_root->data) {
bool return_value = insert(local_root->left, item);
if (return_value){ //we have inserted the item
local_root->update_left_height(); //left height might increase by 1
if (local_root->balance() <= -2) // local root is now critically unbalanced
rebalance_left(local_root);
}
return return_value;
}
else if (local_root->data < item) {
bool return_value = insert(local_root->right, item);
if (return_value){
local_root->update_right_height(); //right height might increase by 1
if (local_root->balance() >= 2) // local root is now critically unbalanced
rebalance_right(local_root);
}
return return_value;
}
else
return false; //item already exists
}
}
void rebalance_left(AVLNode<Item_Type>*& local_root) {
if (local_root->left->balance() > 0) // See whether left-right-heavy
rotate_left(local_root->left); // Perform left rotation
// Finally rotate right
rotate_right(local_root);
}
void rebalance_right(AVLNode<Item_Type>*& local_root) {
if (local_root->right->balance() < 0) // See whether right-left-heavy
rotate_right(local_root->right); // Perform left rotation
// Finally rotate right
rotate_left(local_root);
}
void rotate_right(AVLNode<Item_Type>*& local_root) {
AVLNode<Item_Type>* temp = local_root->left;
local_root->left = temp->right;
//adjust the balances
local_root->update_left_height();
temp->right = local_root;
temp->update_right_height();
local_root = temp;
}
void rotate_left(AVLNode<Item_Type>*& local_root) {
AVLNode<Item_Type>* temp = local_root->right;
local_root->right = temp->left;
//adjust the balances
local_root->update_right_height();
temp->left = local_root;
temp->update_left_height();
local_root = temp;
}
};
#endif
This is the AVL_Node class
#ifndef AVLNODE_H_
#define AVLNODE_H_
#include <sstream>
template<typename Item_Type>
struct AVLNode {
// Additional data field
int right_height;
int left_height;
AVLNode<Item_Type>* left;
AVLNode<Item_Type>* right;
Item_Type data;
// Constructor
AVLNode(const Item_Type& the_data, AVLNode<Item_Type>* left = NULL, AVLNode<Item_Type>* right = NULL) : data(the_data), left(left), right(right), right_height(0), left_height(0) {}
// Destructor (to avoid warning message)
virtual ~AVLNode() {}
int balance(){ return right_height - left_height; }
int height(){
return right_height > left_height ? right_height : left_height; }
void update_right_height(){
if (right != NULL)
right_height = 1 + right->height();
else
right_height = 0;
}
void update_left_height(){
if (left != NULL)
left_height = 1 + left->height();
else
left_height = 0;
}
// to_string
virtual std::string to_string() const {
std::ostringstream os;
os << "data : " << this->data;
return os.str();
}
}; // End AVLNode
#endif
Finally, the class I created, the Folder class:
#pragma once
#include <string>
#include "AVL_Tree.h"
using namespace std;
class Folder
{
private:
string name;
int size;
public:
Folder()
{
name = "";
size = 0;
}
Folder(string Name, int Size)
{
name = Name;
size = Size;
}
int getSize()
{
return size;
}
string getName()
{
return name;
}
void setSize(int Size)
{
size = Size;
}
void setName(string Name)
{
name = Name;
}
};
The error only occurs when I try to do
AVL_Tree<Folder> folderTree;
it works for other types, such as string, int, char, etc. Any help would be greatly appreciated. As far as I know, we are not supposed to modify the instructor's code.

Answer 1

Your class Folder should be "comparable", it means the following code should compile Folder a,b; bool result = (a<b);
To achieve this, you can define the comparison operator withing your class
bool operator< (const Folder & other) const
{
return size < other.size || (size == other.size && name < other.name);
}
Alternatively you can define a global comparison operator bool operator< (const Folder & lhs, const Folder & rhs).