C++ - Insert a new node at the end of the Circular Doubly Linked List

In this method, a new node is inserted at the end of the circular doubly linked list. For example - if the given List is 10->20->30 and a new element 100 is added at the end, the List becomes 10->20->30->100.

Inserting a new node at the end of the circular doubly linked list is very easy. First, a new node with given element is created. It is then added at the end of the list by linking the last node and head node to the new node.

Circular Doubly Linked List - Add Node At End

The function push_back is created for this purpose. It is a 6-step process.

void push_back(int newElement) {
  
  //1. allocate node
  Node* newNode = new Node();
  
  //2. assign data element
  newNode->data = newElement;
  
  //3. assign null to the next and prev
  //   of the new node
  newNode->next = NULL;
  newNode->prev = NULL; 
  
  //4. Check the list is empty or not,
  //   if empty make the new node as head 
  if(head == NULL) {
    head = newNode;
    newNode->next = head;
    newNode->prev = head;
  } else {
    
    //5. Else, traverse to the last node
    Node* temp = head;
    while(temp->next != head)
      temp = temp->next;
    
    //6. Adjust the links
    temp->next = newNode;
    newNode->next = head;
    newNode->prev = temp;
    head->prev = newNode;
  }    
}

The below is a complete program that uses above discussed concept to insert new node at the end of the circular doubly linked list.

#include <iostream>
using namespace std;

//node structure
struct Node {
    int data;
    Node* next;
    Node* prev;
};

class LinkedList {
  private:
    Node* head;
  public:
    LinkedList(){
      head = NULL;
    }
 
    //Add new element at the end of the list
    void push_back(int newElement) {
      Node* newNode = new Node();
      newNode->data = newElement;
      newNode->next = NULL;
      newNode->prev = NULL; 
      if(head == NULL) {
        head = newNode;
        newNode->next = head;
        newNode->prev = head;
      } else {
        Node* temp = head;
        while(temp->next != head)
          temp = temp->next;
        temp->next = newNode;
        newNode->next = head;
        newNode->prev = temp;
        head->prev = newNode;
      }    
    }

    //display the content of the list
    void PrintList() {
      Node* temp = head;
      if(temp != NULL) {
        cout<<"The list contains: ";
        while(true) {
          cout<<temp->data<<" ";
          temp = temp->next;
          if(temp == head) 
            break;
        }
        cout<<endl;
      } else {
        cout<<"The list is empty.\n";
      }
    }     
};

// test the code 
int main() {
  LinkedList MyList;

  //Add three elements at the end of the list.
  MyList.push_back(10);
  MyList.push_back(20);
  MyList.push_back(30);
  MyList.PrintList();
  
  return 0; 
}

The above code will give the following output:

The list contains: 10 20 30