doubly_linked_list.cpp

#include<bits/stdc++.h>
using namespace std;

class Node {
    public:
        int data;
        Node* next;
        Node* prev;

        Node(int val) {
            data = val;
            next = NULL;
            prev = NULL;
        }
};

void insertAtHead(Node* &head, int val) {
    Node* n = new Node(val);
    n->next = head;
    
    if(head!=NULL) {
        head->prev = n;
    }
    
    head = n;
}

void insertAtTail(Node* &head, int val) {
    if(head == NULL) {
        insertAtHead(head, val);
        return;
    }
    
    Node* n = new Node(val);
    Node* temp = head;

    while(temp->next != NULL) {
        temp = temp->next;
    }

    temp->next = n;
    n->prev = temp;
}

void display(Node* head) {
    Node* temp = head;
    while(temp != NULL) {
        cout<<temp->data<<"<->";
        temp = temp->next;
    }

    cout<<"NULL"<<endl;
}

void deleteAtHead(Node* &head) {
    Node* toDelete = head;
    head = head->next;
    head->prev = NULL;

    delete toDelete;
}

void deleteNode(Node* &head, int pos) {
    if(pos == 1) {
        deleteAtHead(head);
        return;
    }

    Node* temp = head;
    int count = 1;

    while(temp!=NULL && count!=pos) {
        temp = temp->next;
        count++;
    }

    temp->prev->next = temp->next;
    if(temp->next != NULL) {
        temp->next->prev = temp->prev;
    }
    delete temp;
}


int main() {

    Node* head = NULL;
    insertAtTail(head, 1);
    insertAtTail(head, 2);
    insertAtTail(head, 3);
    insertAtTail(head, 4);
    
    display(head);
    insertAtHead(head, 5);
    display(head);

    deleteNode(head, 4);
    display(head);

    deleteNode(head, 1);
    deleteAtHead(head);
    display(head);

    return 0;
}