AVL Trees and Doubly Linked Lists - c++

Question

so, I am really new to programming, and I am taking a c++ class right now, in which I need to write and implement and AVL Tree, using a Doubly Linked lists to print off the contents of my tree, level by level. The teacher is really picky, so we can't use any containers from the standard libraries. My Doubly Linked list should be working fine, because I used it on a previous project, but I am getting an error when trying to combine it with the AVL Tree. I know my code probably has A LOT of things that need to be modified, but one step at a time. I am getting the following error, so I was wondering if you guys could help me figure out how to fix it. Also, if you have any suggestions on how to better my code, I would appreciate it.
In instantiation of ‘void AVLTreeSet::print(std::ofstream&) [with ItemType = std::basic_string; std::ofstream = std::basic_ofstream]’:
Lab6/main.cpp:80:20: required from here
Lab6/AVLTreeSet.h:152:49: error: cannot convert ‘LinkedList >::AVLNode*>::Node*’ to ‘AVLTreeSet >::AVLNode*’ in initialization
AVLNode* n = MyList.remove(i);
This is my AVLTree.h:
#pragma once
#include <fstream>
#include "LinkedList.h"
using namespace std;
template <typename ItemType>
class AVLTreeSet {
struct AVLNode {
ItemType item;
int height;
AVLNode* left;
AVLNode* right;
AVLNode(const ItemType& _item, AVLNode* _left = NULL, AVLNode* _right = NULL, int _height = 0) :
item(_item), left(_left), right(_right), height(_height) {}
};
AVLNode* root;
int size = 0;
public:
void RemoveBelowRoot(AVLNode *& n, const ItemType& item)
{
if (n == NULL)
{
return;
}
else if(item < n->item)
{
RemoveBelowRoot(n->left, item);
}
else if(item > n->item)
{
RemoveBelowRoot(n->right, item);
}
else if(n->left == NULL)
{
n = n->right;
}
else if (n->right == NULL)
{
n = n->left;
}
else
{
n = findMin(n->right);
RemoveBelowRoot(n->right, n->item);
}
balance(n);
size--;
// update height of nodes on this path
}
AVLNode * findMin(AVLNode* n)
{
if (n == NULL)
{
return n;
}
else if (n->left->item < n->item)
{
findMin(n->left);
}
else if(n->left->item > n->item)
{
findMin(n->right);
}
return n;
}
void remove(const ItemType& item) {
RemoveBelowRoot(root, item);
}
bool find(const ItemType& item) {
if (findBelowRoot(root, item))
{
return true;
}
return false;
}
bool findBelowRoot(AVLNode * n, const ItemType& data)
{
if (n->item == data)
{
return true;
}
else if (data > n->item)
{
findBelowRoot(n->right, data);
}
else if (data < n->item)
{
findBelowRoot(n->left, data);
}
}
void clear()
{
while (getHeight(root) != 0)
{
// remove
}
}
void addBelowRoot(AVLNode *& n, const ItemType& item)
{
if (n == NULL)
{
n = new AVLNode(item);
size++;
}
else if (item < n->item)
{
addBelowRoot(n->left, item);
}
else if(item > n->item)
{
addBelowRoot(n->right, item);
}
}
void add(const ItemType& item) {
addBelowRoot(root, item);
}
void print (ofstream& out)
{
if (root == NULL)
{
return;
}
else {
LinkedList<AVLNode *> MyList;
MyList.insert(0, root); // add root to Q
while (MyList.getSize() != 0) // While Q is not empty
//(figure out how many items are in that level)(levelsize = Q.size();)
{
for (auto i = 0; i < MyList.getSize(); i++) // for (int 1 = 0; i < LEVELSIZE; i++)
{
AVLNode* n = MyList.remove(i);
out << "level " << i << " " << n->item << "(" << n->height << ") ";
if (n->left != NULL) {
MyList.insert(MyList.getSize(), n->left);
}
if (n->right != NULL) {
MyList.insert(MyList.getSize(), n->right);
}
}
}
out << "\n ";
}
}
void balance (AVLNode *n)
{
if (getHeight(n->left) - getHeight(n->right))
{
balanceToRight(n);
}
if (getHeight(n->right) - getHeight(n->left))
{
balanceToLeft(n);
}
}
int getHeight(AVLNode *& n)
{
if (n == NULL)
{
return 0;
}
else
{
return n->height;
}
}
void balanceToRight(AVLNode * n)
{
if (getHeight(n->left->right) > getHeight(n->left->left))
{
rotateLeft(n->left);
}
rotateRight(n);
}
void rotateRight(AVLNode *&n)
{
AVLNode * k = n->left;
n->left = k->right;
k->right = n;
n = k;
// update heights of k and n
}
void rotateLeft(AVLNode *& n)
{
AVLNode * k = n->right;
n->right = k->left;
k->left = n;
n = k;
// update heights of k and n
}
void balanceToLeft(AVLNode * n)
{
if (getHeight(n->right->left) > getHeight(n->right->right)) // check with TAs if this is right
{
rotateRight(n);
}
rotateLeft(n);
}
/*void updateHeight(AVLNode *& n)
{
}*/
};
Now this is my LinkedList.h
#pragma once
#include <iostream>
#include <cstddef>
#include <fstream>
using namespace std;
template <typename ItemType>
class LinkedList {
struct Node {
ItemType item;
Node *next;
Node *prev;
Node(const ItemType &_item, Node *_next = NULL, Node *_prev = NULL) :
item(_item), next(_next), prev(_prev) { }
};
Node *head;
Node *tail;
int size = 0;
public:
~LinkedList()
{
clear();
}
void insert(int index, ItemType& item) {
if (index > size || size < 0)
{
return;
}
Node * newNode = new Node(item);
if (size == 0)
{
head = newNode;
tail = newNode;
newNode->next = NULL;
newNode->prev = NULL;
size++;
}
else if (index == 0)
{
head->prev = newNode;
newNode->next = head;
head = newNode;
size++;
}
else if (index == size) //INSERTING AT THE END
{
newNode->prev = tail;
newNode->next = NULL;
tail->next = newNode;
tail = newNode;
size++;
}
else {
Node* n = find_node(index);
newNode->next = n;
newNode->prev = n->prev;
n->prev->next = newNode;
n->prev = newNode;
size++;
}
}
Node * remove(int index) {
if (head == NULL || index >= size || index < 0)
{
return NULL;
}
else {
Node* name = find_node(index);
Node * n;
if (size == 1) // REMOVE THE ONLY NODE
{
n = head;
head = NULL;
tail = NULL;
size--;
}
else if (index == 0) //REMOVE THE FIRST NODE WHEN THERE'S MORE THAN ONE IN THE LIST
{
n = head;
head = head->next;
head->prev = NULL;
size--;
}
else if (index == size-1) //REMOVE THE LAST WHEN THERE'S MORE THAN ONE NODE IN THE LIST
{
n = tail;
tail = n->prev;
tail->next = NULL;
size--;
}
else
{
n = find_node(index);
n->prev->next = n->next;
n->next->prev = n->prev;
size--;
}
delete n;
return name;
}
}
Node * find_node(int index)
{
Node * n = NULL;
if (0 <= index && index <= size/2)
{
n = head;
for (int i = 0; i < index; i++)
{
n = n->next;
}
}
else if (size/2 < index && index <= size-1)
{
n = tail;
for (unsigned i = size-1; i > index; i--)
{
n = n->prev;
}
}
return n;
}
int getSize()
{
return size;
}
/* void print(LinkedList <string>& list, ofstream& out, int i)
{
if(head == NULL)
{
return;
}
out << "node " << i << ": " << getItem(i) << "\n";
}
Node* getItem(const int index)
{
if (index > size)
{
return NULL;
}
Node* temp = head;
for (unsigned i = 0; i < size; i++)
{
if (i == index)
{
return temp;
}
temp = temp-> next;
}
return NULL;
}*/
/* int find(const ItemType& item) {
Node * NodeP = head;
for (unsigned i = 0; i < size; i++)
{
if (NodeP->item == item)
{
return i;
}
NodeP = NodeP->next;
}
return -1;
}*/
void clear()
{
while (size != 0){
remove(0);
}
}
};
Thanks so much!

Answer 1

LinkedList::remove returns a LinkedList::Node pointer. You are trying to assign that into an AVLTreeSet::AVLNode pointer.
The AVLTreeSet::AVLNode * you are looking for is in the item member of the returned Node pointer.
You could do something like:
LinkedList<AVLNode *>::Node* n = MyList.remove(i);
AVLNode *treeNode = n->item;
Notes
You should be checking for NULL as the return value for remove, if it doesn't find anything.
remove actually deletes the node then returns it. You are then accessing something that has been deleted, which is Undefined Behavior. You really need to fix this before you go much further.
your for loop will only remove about half of the objects, as your are removing items from the list while still iterating further along the list using i.