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

# C++ Linked List Exercises: Insert new node at the middle of a Doubly Linked List

## C++ Linked List: Exercise-21 with Solution

Write a C++ program to insert a new node at the middle of a given Doubly Linked List.

Test Data:
Doubly linked list is as follows:
---------------------------------
Traversal in Forward direction: Orange White Green Red
Traversal in Reverse direction: Red Green White Orange
Insert a new node at the middle position of the said Doubly linked list:
-----------------------------------------------------------------------
Traversal in Forward direction: Orange White Pink Green Red
Traversal in Reverse direction: Red Green Pink White Orange
Insert another new node at the middle position of the said Doubly linked list:
-----------------------------------------------------------------------------
Traversal in Forward direction: Orange White Pink Black Green Red
Traversal in Reverse direction: Red Green Black Pink White Orange

Sample Solution:

C++ Code:

``````#include <iostream> // Including input-output stream header file

using namespace std; // Using standard namespace

// A doubly linked list node
struct Node {
string data; // Data field to store string data
struct Node* next; // Pointer to the next node
struct Node* prev; // Pointer to the previous node
};

// Function to append data at the front of the doubly linked list
{
// Create a new node and allocate memory.
struct Node* newNode = new Node;

// Assign data to new node
newNode->data = new_data;

// A new node has been added with the name head and the previous node
// set to null, since it is being added at the front.
newNode->prev = NULL;

// Previous head is the new node

// Head points to the new node
}

// Function to insert a node at the middle position of the doubly linked list
Node* new_Node = new Node(); // Creating a new node
new_Node->data = data; // Assigning data to the new node

return; // If the linked list is empty, return
}

int size = 0;

// Calculate length of the linked list, i.e., the number of nodes
while (ptr != NULL) {
size++;
ptr = ptr->next;
}

// Find middle position
int mid_pos = (size % 2 == 0) ? (size/2) : (size+1)/2;
if(mid_pos == size){
new_Node->next = NULL;
size++;
return;
}

while(--mid_pos){
temp = temp->next;
}

(temp->next)->prev = new_Node;
new_Node->prev = temp;
new_Node->next = temp->next;
temp->next = new_Node;
size++;
}

// Following function displays contents of the doubly linked list
{
Node* last_node;
cout << "\nTraversal in Forward direction: ";
cout << " " << head->data << " "; // Displaying data in forward direction
}
cout << "\nTraversal in Reverse direction: ";
while (last_node != NULL) {
cout << " " << last_node->data << " "; // Displaying data in reverse direction
last_node = last_node->prev;
}
}

// Main program
int main() {
append_data(&head, "Red"); // Appending "Red" at the front of the list
append_data(&head, "Green"); // Appending "Green" at the front of the list
append_data(&head, "White"); // Appending "White" at the front of the list
append_data(&head, "Orange"); // Appending "Orange" at the front of the list
cout<<"Doubly linked list is as follows: ";
cout<<"\n---------------------------------";
cout<<"\n\nInsert a new node at the middle position of the said Doubly linked list:";
cout<<"\n-----------------------------------------------------------------------";
insertAtMid(&head, "Pink"); // Inserting "Pink" node at the middle of the list
cout<<"\n\nInsert another new node at the middle position of the said Doubly linked list:";
cout<<"\n-----------------------------------------------------------------------------";
insertAtMid(&head, "Black"); // Inserting "Black" node at the middle of the list
cout<<endl;
return 0; // Returning from the main function
}
``````

Sample Output:

```Doubly linked list is as follows:
---------------------------------
Traversal in Forward direction:  Orange  White  Green  Red
Traversal in Reverse direction:  Red  Green  White  Orange

Insert a new node at the middle position of the said Doubly linked list:
-----------------------------------------------------------------------
Traversal in Forward direction:  Orange  White  Pink  Green  Red
Traversal in Reverse direction:  Red  Green  Pink  White  Orange

Insert another new node at the middle position of the said Doubly linked list:
-----------------------------------------------------------------------------
Traversal in Forward direction:  Orange  White  Pink  Black  Green  Red
Traversal in Reverse direction:  Red  Green  Black  Pink  White  Orange

```

Flowchart:

CPP Code Editor: