Remove duplicates from an unsorted linked list

LinkedList-RemoveDuplicates.cpp

#include<iostream>
#include<set>
using namespace std;

class Node {
public:
    int data;
    Node *next;
    Node(int dat) {
        data = dat;
        next = NULL;
    }
};

class LinkedList {
public:
    Node *head;
    Node *tail;
    int length;
    
    LinkedList() {
        head = NULL;
        tail = NULL;
        length = 0;
    }
    ~LinkedList() {
        destory();
    }
    Node* createANode(int dat);
    void makeAList(int a[], int size);
    void insertNodeAt(int dat, int index);
    void deleteNodeAt(int index);
    void printList(Node *h = NULL);
    void destory(Node *h = NULL);
    void removeDuplicates() {
        set<int> testSet;
        pair<set<int>::iterator, bool> result;
        Node *tempPrev = NULL;
        Node *temp = head;
        int i = 0;
        while(temp != NULL) {
            result = testSet.insert(temp->data);
            if (result.second == false) {
                temp = tempPrev;
                deleteNodeAt(i);
                i--;
            }
            i++;
            tempPrev = temp;
            temp = temp->next;
        }
    }
};

Node* LinkedList::createANode(int dat) {
    Node *newNode = (Node *)malloc(sizeof(Node));
    newNode->data = dat;
    newNode->next = NULL;
    return newNode;
}

void LinkedList::makeAList(int a[], int size) {
    if (head != NULL) return;
    for (int i = 0; i < size; i++) {
        Node *temp = createANode(a[i]);
        if (i == 0) {
            head = temp;
            tail = temp;
            length++;
        } else {
            tail->next = temp;
            tail = temp;
            length++;
        }
    }
}

void LinkedList::insertNodeAt(int dat, int index) {
    if (index < 0 || index  > length) return;
    Node *temp = createANode(dat);
    Node *insertPPrev = NULL;
    Node *insertP = head;
    for (int i = 0; i < index; i++) {
        insertPPrev = insertP;
        insertP = insertP->next;
    }
    // insert at head
    if (insertPPrev == NULL) {
        temp->next = head;
        head = temp;
        // insert at tail
    } else if (insertP == NULL) {
        insertPPrev->next = temp;
        tail = temp;
    } else {
        insertPPrev->next = temp;
        temp->next = insertP;
    }
    length++;
}

void LinkedList::deleteNodeAt(int index) {
    if (index < 0 || index >= length) return;
    Node *deletePPrev = NULL;
    Node *deleteP = head;
    for (int i = 0; i < index; i++) {
        deletePPrev = deleteP;
        deleteP = deleteP->next;
    }
    length--;
    // the only node is deleted
    if (length == 0) {
        free(head);
        head = NULL;
        tail = NULL;
        return;
    }
    // at least one node is there
    // delete at head
    if (deletePPrev == NULL) {
        head = head->next;
        free(deleteP);
    } else if (deleteP == tail) {
        tail = deletePPrev;
        tail->next = NULL;
        free(deleteP);
    } else {
        deletePPrev->next = deleteP->next;
        free(deleteP);
    }
}

void LinkedList::printList(Node *h) {
    Node *theHead = NULL;
    if (h != NULL){
        theHead = h;
    } else {
        theHead = head;
    }
    while(theHead != NULL) {
        cout << theHead->data << " -> ";
        theHead = theHead->next;
    }
    cout << "NULL\n";
}

void LinkedList::destory(Node *h) {
    Node *theHead = NULL;
    if (h != NULL) {
        theHead = h;
    } else {
        theHead = head;
    }
    Node *temp;
    while (theHead != NULL) {
        temp = theHead;
        theHead = theHead->next;
        free(temp);
    }
    head = NULL;
    tail = NULL;
    length = 0;
}

int main() {
    int a[] = {1,2,3,4,5,6,7,8};
    LinkedList list = LinkedList();
    list.makeAList(a, 8);
    list.printList();
    list.insertNodeAt(10,8);
    list.insertNodeAt(10,2);
    list.insertNodeAt(7,2);
    list.printList();
    list.removeDuplicates();
    list.printList();
    list.destory();
    return 0;
}