DEV Community: Divyanshu Singh

doubly linked list- implementation, insertion(head and tail), printing, reverse printing and deletion

Divyanshu Singh — Tue, 12 May 2026 17:11:51 +0000

#include <iostream>
using namespace std;
struct Node
{
    int data;
    Node* next;
    Node* prev;
};
Node* head;
Node* GetNewNode(int x)
{
    Node* newNode = new Node();
    newNode->data = x;
    newNode->next = NULL;
    newNode->prev = NULL;
    return newNode;
}
void InsertAtHead(int x)
{
    Node* newNode = GetNewNode(x);
    if(head == NULL)
    {
        head = newNode;
        return;
    }
    head->prev = newNode;
    newNode->next = head;
    head = newNode;   
}
void InsertAtTail(int x)
{
    Node* newNode = GetNewNode(x);
    if(head == NULL)
    {
        head = newNode;
        return;
    }
    Node* temp = head;
    while(temp->next != NULL)
    {
        temp = temp->next;
    }
    temp->next = newNode;
    newNode->prev = temp;

}
void print()
{
    Node* temp = head;
    while(temp != NULL)
    {
        cout<<temp-> data<<" ";
        temp = temp->next;
    }
    cout<<endl;
}
void reversePrint()
{
    Node* temp = head;
    while(temp->next != NULL)
    {
        temp = temp->next;
    }
    while(temp != NULL)
    {
        cout<<temp->data<<" ";
        temp = temp->prev;
    }
    cout<<endl;
}
void deleted(int pos)
{
    // Case 1: empty list
    if(head == NULL)
    {
        cout << "List is empty\n";
        return;
    }

    Node* temp = head;

    // Case 2: delete head
    if(pos == 1)
    {
        head = temp->next;

        if(head != NULL)
            head->prev = NULL;

        delete temp;
        return;
    }

    // Traverse to pos-th node
    for(int i = 1; i < pos; i++)
    {
        if(temp == NULL)
        {
            cout << "Invalid position\n";
            return;
        }
        temp = temp->next;
    }

    if(temp == NULL)
    {
        cout << "Invalid position\n";
        return;
    }

    // Re-link neighbors
    if(temp->prev != NULL)
        temp->prev->next = temp->next;

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

    delete temp;
}
int main()
{
    head = NULL;
    InsertAtHead(1);
    InsertAtHead(2);
    InsertAtHead(3);
    print();
    reversePrint();
    InsertAtTail(4);
    InsertAtTail(5);
    InsertAtTail(6);
    print();
    reversePrint();
    deleted(2);
    print();
}

reversing a linked list

Divyanshu Singh — Tue, 12 May 2026 15:46:41 +0000

#include <iostream>
using namespace std;
struct Node
{
    int data;
    Node* next;
};
Node* head;
void insertAtNthPosition(int x, int pos)
{

   Node* temp1 = new Node();
   temp1->data = x;
   if(pos == 1)
   {
       temp1->next = head;
       head = temp1;
       return;
   }
   temp1->next = NULL;
   Node* temp2 = head;
   for(int i = 0; i<pos-2; i++)
   {
       if(temp2 == NULL)
       {
           cout<< "INVALID POSITION\n";
           return;
       }
       temp2 = temp2->next;
    }
    if(temp2 == NULL)
       {
           cout<< "INVALID POSITION\n";
           return;
       }  
    temp1->next = temp2->next;
    temp2->next = temp1;
}
void print()
{
    Node* temp = head;
    cout<<"The list:\n";
    while(temp != NULL)
    {
        cout<< temp->data << " ";
        temp = temp->next;
    }
    cout<< endl;
}
void reverse()
{
    Node* prev = NULL;
    Node* current = head;
    Node* next;
    while(current != NULL)
    {
        next = current->next;
        current->next = prev;
        prev = current;
        current = next;
    }
    head = prev;
}
int main()
{
    head = NULL;
    int n, pos, x;
    cout << "How many elements do you want to insert and at a random position?\n";
    cin>>n;
    for(int i = 0; i<n; i++)
    {
    cout<< "Enter the element and the position of the element\n";
    cin>>x>>pos;
    insertAtNthPosition(x,pos);
    print();
    }
    cout<< "The reversed list is:\n";
    reverse();
    print();
}

deleting a node at nth position in a linked list

Divyanshu Singh — Tue, 12 May 2026 11:30:41 +0000

#include <iostream>
using namespace std;
struct Node
{
    int data;
    Node* next;
};
Node* head;
void insertAtNthPosition(int x, int pos)
{

   Node* temp1 = new Node();
   temp1->data = x;
   if(pos == 1)
   {
       temp1->next = head;
       head = temp1;
       return;
   }
   temp1->next = NULL;
   Node* temp2 = head;
   for(int i = 0; i<pos-2; i++)
   {
       if(temp2 == NULL)
       {
           cout<< "INVALID POSITION\n";
           return;
       }
       temp2 = temp2->next;
    }
    if(temp2 == NULL)
       {
           cout<< "INVALID POSITION\n";
           return;
       }  
    temp1->next = temp2->next;
    temp2->next = temp1;
}
void print()
{
    Node* temp = head;
    cout<<"The list:\n";
    while(temp != NULL)
    {
        cout<< temp->data << " ";
        temp = temp->next;
    }
    cout<< endl;
}
void deleted(int pos)
{
    Node* temp1 = head;
    if(head == NULL)
    {
        cout<<"INVALID POSITION\n";
        return;
    }
    if(pos == 1)
    {
        head = temp1->next;
        delete temp1;
        return;
    } 
    for(int i = 0; i < pos-2; i++)
    {
        temp1 = temp1->next;
    }
    Node* temp2 = temp1->next;
    if(temp2 == NULL)
    {
        cout<<"INVALID POSITION\n";
        return;
    }
    temp1->next = temp2->next;
    delete temp2;
}

int main()
{
    head = NULL;
    int n, pos, x;
    cout << "How many elements do you want to insert and at a random position?\n";
    cin>>n;
    for(int i = 0; i<n; i++)
    {
    cout<< "Enter the element and the position of the element\n";
    cin>>x>>pos;
    insertAtNthPosition(x,pos);
    print();
    }
    cout<< "Enter a position of node to be deleted?\n";
    cin>>pos;
    deleted(pos);
    print();
}

inserting elements at nth position in a linked list

Divyanshu Singh — Tue, 12 May 2026 10:54:04 +0000

#include <iostream>
using namespace std;
struct Node
{
    int data;
    Node* next;
};
Node* head;
void insertAtNthPosition(int x, int pos)
{

   Node* temp1 = new Node();
   temp1->data = x;
   if(pos == 1)
   {
       temp1->next = head;
       head = temp1;
       return;
   }
   temp1->next = NULL;
   Node* temp2 = head;
   for(int i = 0; i<pos-2; i++)
   {
       if(temp2 == NULL)
       {
           cout<< "INVALID POSITION\n";
           return;
       }
       temp2 = temp2->next;
    }
    if(temp2 == NULL)
       {
           cout<< "INVALID POSITION\n";
           return;
       }  
    temp1->next = temp2->next;
    temp2->next = temp1;
}
void print()
{
    Node* temp = head;
    cout<<"The list:\n";
    while(temp != NULL)
    {
        cout<< temp->data << " ";
        temp = temp->next;
    }
    cout<< endl;

}
int main()
{
    head = NULL;
    int n, pos, x;
    cout << "How many elements do you want to insert and at a random position?\n";
    cin>>n;
    for(int i = 0; i<n; i++)
    {
    cout<< "Enter the element and the position of the element\n";
    cin>>x>>pos;
    insertAtNthPosition(x,pos);
    print();
    }
}

inserting elements at beginning of a linked list

Divyanshu Singh — Tue, 12 May 2026 08:55:59 +0000

#include <iostream>
using namespace std;
struct Node
{
    int data;
    Node* next;
};
Node* head;
void insertAtBeginning(int x)
{
   Node* temp = new Node();
   temp->data = x;
//   temp->next = NULL;
//   if(head != NULL)
//   {
//       temp->next = head;

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

}
int main()
{
    head = NULL;
    int n, x;
    cout << "How many elements do you want to insert at the beginning?\n";
    cin>>n;
    for(int i = 0; i<n; i++)
    {
    cout<< "Enter the element\n";
    cin>>x;
    cout<<"The list after adding "<<x<<" is:\n";
    insertAtBeginning(x);
    print();
    }
}