# Find middle element in doubly linked list

Finding the middle element in a doubly linked list means to determine the node that is positioned exactly in the middle of the list. In a doubly linked list, each node has two pointers, one pointing to the previous node and the other pointing to the next node.

To find the middle element of a doubly linked list, you need to traverse the list by starting from the head node and moving towards the tail node. During this traversal, you need to keep two pointers, a slow pointer and a fast pointer.

The slow pointer moves one node at a time, whereas the fast pointer moves two nodes at a time. When the fast pointer reaches the end of the list, the slow pointer will be pointing to the middle node.

If the doubly linked list contains an even number of nodes, then there are two possible middle nodes. In this case, you can choose either of the middle nodes.

## Program List

``````//C Program
//Find middle element in doubly linked list
#include <stdio.h>

#include <stdlib.h> //for malloc function

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

struct Node *head = NULL, *tail = NULL;

//insert Node element of end of linked list
void insert(int value) {

//Create a dynamic Node
struct Node *node = (struct Node *) malloc(sizeof(struct Node));
if (node == NULL) {
printf("Memory overflow\n");
} else {
//set data value
node->data = value;
node->next = NULL;
node->prev = NULL;
tail = node;

} else {
node->prev = tail;
tail->next = node;

tail = node;

}
}
}
//display element of Node
void display() {
if (temp == NULL) {
} else {

printf("\n Head to Tail Nodes : \n");
//Traverse doubly linked list from front to rear
while (temp != NULL) {
//print Node value
printf("%3d", temp->data);
temp = temp->next;
}
printf("\n Tail to Head Nodes : \n");

temp = tail;

//Traverse doubly linked list from rear to front
while (temp != NULL) {
//print Node value
printf("%3d", temp->data);
temp = temp->prev;
}
}

}
///find mid node
void  middle_node()
{

{

while(fast!=NULL && fast->next != NULL && fast->next->next != NULL)
{
slow = slow->next;
fast = fast->next->next;
}
printf("\n Middle : %d\n",slow->data);

}else
{

}
}

int main() {

insert(1);
insert(2);
insert(3);
insert(4);
insert(5);
insert(6);
//Display all node
display();

middle_node();

insert(7);
display();
middle_node();
printf("\n");
return 0;
}```
```

#### Output

`````` Head to Tail Nodes :
1  2  3  4  5  6
6  5  4  3  2  1
Middle : 3

1  2  3  4  5  6  7
7  6  5  4  3  2  1
Middle : 4
``````
``````/*
C++ Program
Find middle element in doubly linked list
*/

#include<iostream>

using namespace std;
class Node {
public:
int data;
Node *next;
Node *prev;
Node(int value) {
this->data = value;
this->next = NULL;
this->prev = NULL;
}
};
public:
Node *tail;
this->tail = NULL;
}
void insert(int value) {
Node *node = new Node(value);
if (node == NULL) {
cout << "Memory overflow\n";
return;
}
this->tail = node;
} else {
node->prev = this->tail;
this->tail->next = node;
this->tail = node;
}
}
void display() {
if (temp == NULL) {
return;
}
cout << "\n Head to Tail Nodes : \n  ";
while (temp != NULL) {
cout << temp->data << "  ";
temp = temp->next;
}
temp = this->tail;
cout << "\n Tail to Head Nodes : \n  ";
while (temp != NULL) {
cout << temp->data << "  ";
temp = temp->prev;
}
}
void middle_node() {
while (fast != NULL && fast->next != NULL && fast->next->next != NULL) {
slow = slow->next;
fast = fast->next->next;
}
cout << "\n Middle : " << slow->data << "\n";
} else {
}
}
};
int main() {
obj.insert(1);
obj.insert(2);
obj.insert(3);
obj.insert(4);
obj.insert(5);
obj.insert(6);
obj.display();
obj.middle_node();
obj.insert(7);
obj.display();
obj.middle_node();
return 0;
}```
```

#### Output

`````` Head to Tail Nodes :
1  2  3  4  5  6
6  5  4  3  2  1
Middle : 3

1  2  3  4  5  6  7
7  6  5  4  3  2  1
Middle : 4
``````
``````/*
Java Program
Find middle element in doubly linked list

*/
class Node {

public int data;

public Node next;

public Node prev;

public Node(int value) {
//Setup initial values of linked list node
this.data = value;
this.next = null;
this.prev = null;
}
}

public Node tail;

tail = null;
}
public void insert(int value) {
Node node = new Node(value);

if (node == null) {

System.out.print("Memory overflow\n");
return;
}
tail = node;
} else {
node.prev = tail;
tail.next = node;
tail = node;
}
}

public void display() {
if (temp == null) {
return;
}

System.out.print("\n Head to Tail Nodes : \n  ");

while (temp != null) {
System.out.print(temp.data + "  ");
temp = temp.next;
}

temp = tail;

System.out.print("\n Tail to Head Nodes : \n  ");

while (temp != null) {
System.out.print(temp.data + "  ");
temp = temp.prev;
}

}
//Find out middle node
public void middle_node() {

while (fast != null && fast.next != null && fast.next.next != null) {
slow = slow.next;
fast = fast.next.next;
}

System.out.print("\n Middle : " + slow.data+ "\n");
} else {

}
}

public static void main(String[] args) {
obj.insert(1);
obj.insert(2);
obj.insert(3);
obj.insert(4);
obj.insert(5);
obj.insert(6);
//Display all node
obj.display();

obj.middle_node();

obj.insert(7);
obj.display();
obj.middle_node();

}

}```
```

#### Output

`````` Head to Tail Nodes :
1  2  3  4  5  6
6  5  4  3  2  1
Middle : 3

1  2  3  4  5  6  7
7  6  5  4  3  2  1
Middle : 4
``````
``````/*
C# Program
Find middle element in doubly linked list

*/
using System;
public class Node {

public int data;

public Node next;

public Node prev;

public Node(int value) {
//Setup initial values of linked list node
this.data = value;
this.next = null;
this.prev = null;
}
}

public Node tail;

tail = null;
}
public void insert(int value) {
Node node = new Node(value);

if (node == null) {

Console.Write("Memory overflow\n");
return;
}
tail = node;
} else {
node.prev = tail;
tail.next = node;
tail = node;
}
}

public void display() {
if (temp == null) {
return;
}

Console.Write("\n Head to Tail Nodes : \n  ");

while (temp != null) {
Console.Write(temp.data + "  ");
temp = temp.next;
}

temp = tail;

Console.Write("\n Tail to Head Nodes : \n  ");

while (temp != null) {
Console.Write(temp.data + "  ");
temp = temp.prev;
}

}
//Find out middle node
public void middle_node() {

while (fast != null && fast.next != null && fast.next.next != null) {
slow = slow.next;
fast = fast.next.next;
}

Console.Write("\n Middle : " + slow.data+ "\n");
} else {

}
}

public static void Main(String[] args) {
obj.insert(1);
obj.insert(2);
obj.insert(3);
obj.insert(4);
obj.insert(5);
obj.insert(6);
//Display all node
obj.display();

obj.middle_node();

obj.insert(7);
obj.display();
obj.middle_node();

}

}```
```

#### Output

`````` Head to Tail Nodes :
1  2  3  4  5  6
6  5  4  3  2  1
Middle : 3

1  2  3  4  5  6  7
7  6  5  4  3  2  1
Middle : 4
``````
``````# Python 3 Program
# Find middle element in doubly linked list

class Node :

def __init__(self, value) :
self.data = value
self.next = None
self.prev = None

def __init__(self) :
self.tail = None

def insert(self, value) :
node = Node(value)
if (node == None) :
print("Memory overflow\n")
return

self.tail = node
else :
node.prev = self.tail
self.tail.next = node
self.tail = node

def display(self) :
if (temp == None) :
return

print("\n Head to Tail Nodes :  ")
while (temp != None) :
print(temp.data ,end="  ")
temp = temp.next

temp = self.tail
print("\n Tail to Head Nodes :  ")
while (temp != None) :
print(temp.data ,end="  ")
temp = temp.prev

def middle_node(self) :
while (fast != None and fast.next != None and fast.next.next != None) :
slow = slow.next
fast = fast.next.next

print("\n Middle : ", slow.data )
else :

def main() :
obj.insert(1)
obj.insert(2)
obj.insert(3)
obj.insert(4)
obj.insert(5)
obj.insert(6)
obj.display()
obj.middle_node()
obj.insert(7)
obj.display()
obj.middle_node()

if __name__ == "__main__":
main()```
```

#### Output

`````` Head to Tail Nodes :
1  2  3  4  5  6
6  5  4  3  2  1
Middle : 3

1  2  3  4  5  6  7
7  6  5  4  3  2  1
Middle : 4
``````
``````# Ruby Program
# Find middle element in doubly linked list

class Node
attr_accessor :data, :next, :prev
def initialize(value)
self.data = value
self.next = nil
self.prev = nil
end
end

def initialize()
@tail = nil
end
def insert(value)
node = Node.new(value)
if (node == nil)
print("Memory overflow\n")
return
end
@tail = node
else
node.prev = @tail
@tail.next = node
@tail = node
end
end
def display()
if (temp == nil)
return
end
print("\n Head to Tail Nodes  :\n  ")
while (temp != nil)
print(temp.data ,"  ")
temp = temp.next
end
temp = @tail
print("\n Tail to Head Nodes  :\n  ")
while (temp != nil)
print(temp.data ,"  ")
temp = temp.prev
end
end
def middle_node()
while (fast != nil and fast.next != nil and fast.next.next != nil)
slow = slow.next
fast = fast.next.next
end
print("\n Middle  : ", slow.data ,"\n")
else
end
end
end
def main()
obj.insert(1)
obj.insert(2)
obj.insert(3)
obj.insert(4)
obj.insert(5)
obj.insert(6)
obj.display()
obj.middle_node()
obj.insert(7)
obj.display()
obj.middle_node()
end

main()```
```

#### Output

`````` Head to Tail Nodes :
1  2  3  4  5  6
6  5  4  3  2  1
Middle : 3

1  2  3  4  5  6  7
7  6  5  4  3  2  1
Middle : 4
``````
``````<?Php
/*
Php Program
Find middle element in doubly linked list
*/

class Node {
public \$data;
public \$next;
public \$prev;

function __construct(\$value) {
\$this->data = \$value;
\$this->next = null;
\$this->prev = null;
}
}
public \$tail;

function __construct() {
\$this->tail = null;
}
public  function insert(\$value) {
\$node = new Node(\$value);
if (\$node == null) {
echo("Memory overflow\n");
return;
}
\$this->tail = \$node;
} else {
\$node->prev = \$this->tail;
\$this->tail->next = \$node;
\$this->tail = \$node;
}
}
public  function display() {
if (\$temp == null) {
return;
}
echo("\n Head to Tail Nodes : \n  ");
while (\$temp != null) {
echo(\$temp->data ."  ");
\$temp = \$temp->next;
}
\$temp = \$this->tail;
echo("\n Tail to Head Nodes : \n  ");
while (\$temp != null) {
echo(\$temp->data ."  ");
\$temp = \$temp->prev;
}
}
public  function middle_node() {
while (\$fast != null && \$fast->next != null && \$fast->next->next != null) {
\$slow = \$slow->next;
\$fast = \$fast->next->next;
}
echo("\n Middle : ". \$slow->data ."\n");
} else {
}
}
}

function main() {
\$obj->insert(1);
\$obj->insert(2);
\$obj->insert(3);
\$obj->insert(4);
\$obj->insert(5);
\$obj->insert(6);
\$obj->display();
\$obj->middle_node();
\$obj->insert(7);
\$obj->display();
\$obj->middle_node();
}
main();```
```

#### Output

`````` Head to Tail Nodes :
1  2  3  4  5  6
6  5  4  3  2  1
Middle : 3

1  2  3  4  5  6  7
7  6  5  4  3  2  1
Middle : 4
``````
``````/*
Node Js Program
Find middle element in doubly linked list
*/

class Node {

constructor(value) {
this.data = value;
this.next = null;
this.prev = null;
}
}

constructor() {
this.tail = null;
}
insert(value) {
var node = new Node(value);
if (node == null) {
process.stdout.write("Memory overflow\n");
return;
}
this.tail = node;
} else {
node.prev = this.tail;
this.tail.next = node;
this.tail = node;
}
}
display() {
if (temp == null) {
return;
}
process.stdout.write("\n Head to Tail Nodes : \n  ");
while (temp != null) {
process.stdout.write(temp.data + "  ");
temp = temp.next;
}
temp = this.tail;
process.stdout.write("\n Tail to Head Nodes : \n  ");
while (temp != null) {
process.stdout.write(temp.data + "  ");
temp = temp.prev;
}
}
middle_node() {
while (fast != null && fast.next != null && fast.next.next != null) {
slow = slow.next;
fast = fast.next.next;
}
process.stdout.write("\n Middle : " + slow.data + "\n");
} else {
}
}
}

function main() {
obj.insert(1);
obj.insert(2);
obj.insert(3);
obj.insert(4);
obj.insert(5);
obj.insert(6);
obj.display();
obj.middle_node();
obj.insert(7);
obj.display();
obj.middle_node();
}

main();```
```

#### Output

`````` Head to Tail Nodes :
1  2  3  4  5  6
6  5  4  3  2  1
Middle : 3

1  2  3  4  5  6  7
7  6  5  4  3  2  1
Middle : 4
``````
``````/*
Swift 4 Program
Find middle element in doubly linked list
*/

class Node {
var data: Int;
var next: Node? ;
var prev: Node? ;
init(_ value: Int) {
self.data = value;
self.next = nil;
self.prev = nil;
}
}
var tail: Node? ;
init() {
self.tail = nil;
}
func insert(_ value: Int) {
let node: Node? = Node(value);
if (node == nil) {
print("Memory overflow\n");
return;
}
self.tail = node;
} else {
node!.prev = self.tail;
self.tail!.next = node;
self.tail = node;
}
}
func display() {
if (temp == nil) {
return;
}
print("\n Head to Tail Nodes :  ");
while (temp != nil) {
print(temp!.data ,terminator:"  ");
temp = temp!.next;
}
temp = self.tail;
print("\n Tail to Head Nodes : ");
while (temp != nil) {
print(temp!.data ,terminator:"  ");
temp = temp!.prev;
}
}
func middle_node() {
while (fast != nil && fast!.next != nil && fast!.next!.next != nil) {
slow = slow!.next;
fast = fast!.next!.next;
}
print("\n Middle : ", slow!.data ,"\n");
} else {
}
}
}
func main() {
obj.insert(1);
obj.insert(2);
obj.insert(3);
obj.insert(4);
obj.insert(5);
obj.insert(6);
obj.display();
obj.middle_node();
obj.insert(7);
obj.display();
obj.middle_node();
}
main();```
```

#### Output

`````` Head to Tail Nodes :
1  2  3  4  5  6
6  5  4  3  2  1
Middle : 3

1  2  3  4  5  6  7
7  6  5  4  3  2  1
Middle : 4
``````

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