Question

In C++

Create a data structure doubly linked list, implement the following operations for the doubly linked list：

addFirst

addLast

insertBefore

insertAfter

delete

printList

Answer 1

#include <stdio.h>
#include <string.h>
#include <iostream>
#include <iomanip>

using namespace std;

//Node Class
class Node{
public:
    double v;
    Node *next;
    Node *prev;
};

//LinkedList class
class LList{
    //Head pointer
    Node *head=nullptr;
    Node *tail = nullptr;
public:
    //This adds a new node at the end of linked list
    void addFirst(double val){
        Node *nnode = new Node();
        nnode->v = val;
        if(head==nullptr){
            head = nnode;
            tail = nnode;
            return;
        }

        nnode->next = head;
        head->prev = nnode;
        head = nnode;
    }

    //This adds a new node at the end of linked list
    void addLast(double val){
        Node *nnode = new Node();
        nnode->v = val;
        if(head==nullptr){
            head = nnode;
            tail = nnode;
            return;
        }
        tail->next = nnode;
        nnode->prev = tail;
        nnode->next = nullptr;
        tail = nnode;
    }

    void insertBefore(double target, double val){
        Node *nnode = new Node();
        nnode->v = val;
        if(head->v==target){
            nnode->next = head;
            head->prev = nnode;
            head = nnode;
            return;
        }
        Node *temp = head;
        while(temp!=nullptr){
            if(temp->v==target){
                Node *prev = temp->prev;
                prev->next = nnode;
                nnode->prev = prev;
                nnode->next = temp;
                temp->prev = nnode;
                break;
            }
            temp = temp->next;
        }
    }

    void insertAfter(double target, double val){
        Node *nnode = new Node();
        nnode->v = val;
        if(target==tail->v){
            tail->next = nnode;
            nnode->prev = tail;
            nnode->next = nullptr;
            tail = nnode;
            return;
        }
        Node *temp = head;
        while(temp!=nullptr){
            if(temp->v==target){
                Node *nxt = temp->next;
                temp->next = nnode;
                nnode->prev = temp;
                nnode->next = nxt;
                nxt->prev = nnode;
                break;
            }
            temp = temp->next;
        }
    }

    //This deletes head node
    void deleteNode(double val){
        if(head->v==val){
            Node *temp = head;
            head = head->next;
            head->prev = nullptr;
            free(temp);
            return;
        }
        if(tail->v==val){
            Node *temp = tail;
            tail = tail->prev;
            tail->next = nullptr;
            free(temp);
            return;
        }
        Node *temp = head;
        while(temp!=nullptr){
            if(temp->v==val){
                Node *prev = temp->prev;
                Node *nxt = temp->next;
                prev->next = nxt;
                nxt->prev = prev;
                free(temp);
                break;
            }
            temp = temp->next;
        }
    }

    //This prints the linked list
    void print(){
        Node *temp = head;
        while(temp!=nullptr){
            cout<<temp->v<<"->";
            temp = temp->next;
        }
        cout<<"NULL"<<endl;
    }
};

int main(){
    LList a;
    a.addFirst(3);
    a.addLast(4);
    a.addFirst(2);
    a.addLast(5);
    a.print();
    a.insertAfter(4,6);
    a.insertBefore(3,7);
    a.insertBefore(2,1);
    a.print();
    a.deleteNode(4);
    a.deleteNode(1);
    a.print();
    return 0;
}

OUTPUT :