﻿ C++ - Middle element of a Doubly Linked List

# C++ Linked List Exercises: Middle element of a Doubly Linked List

## C++ Linked List: Exercise-20 with Solution

Write a C++ program to find the middle element 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
The middle element is: Green
Insert a new node at the end of a Doubly Linked List:
-------------------------------------------------------------
Traversal in Forward direction: Pink Orange White Green Red
Traversal in Reverse direction: Red Green White Orange Pink
The middle element is: White

Sample Solution:

C++ Code:

``````#include <iostream>

using namespace std;

// A doubly linked list node
struct Node {
string data;
struct Node* next;
struct Node* prev;
};

//Append node at the front of the 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;

}

{

{
while (fastptr != NULL && fastptr->next != NULL)
{
fastptr = fastptr->next->next;
slowptr = slowptr->next;
}
cout<<"\nThe middle element is: "<<slowptr->data;
}
}

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

//main program
int main() {
cout<<"Doubly linked list is as follows: ";
cout<<"\n---------------------------------";
cout<<"\n\nInsert a new node:";
cout<<"\n--------------------";
cout<<endl;
return 0;
}
``````

Sample Output:

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

Insert a new node:
--------------------
Traversal in Forward direction:  Pink  Orange  White  Green  Red
Traversal in Reverse direction:  Red  Green  White  Orange  Pink
The middle element is: White
```

Flowchart:

CPP Code Editor:

Previous C++ Exercise: Insert a new node at the end of a Doubly Linked List.
Next C++ Exercise: Insert new node at the middle of a Doubly Linked List.

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## C++ Programming: Tips of the Day

How to replace all occurrences of a character in string?

std::string doesn't contain such function but you could use stand-alone replace function from algorithm header.

```#include <algorithm>
#include <string>

void some_func() {
std::string s = "example string";
std::replace( s.begin(), s.end(), 'x', 'y'); // replace all 'x' to 'y'
}
```

Ref: https://bit.ly/3niU71x