Circular Doubly Linked List - Traversal

Traversing through a circular doubly linked list is very easy. It requires creating a temp node pointing to the head of the list. If the temp node is not null, display its content and move to the next node using temp next. Repeat the process till the temp node reaches the starting node (head of the list). If the temp node is empty at the start, then the list contains no item.

A circular doubly linked list can be traversed from any node as the starting point. Traverse the list till reaches the same node.

The function PrintList is created for this purpose. It is a 3-step process.

```void PrintList() {

//1. create a temp node pointing to head

//2. if the temp node is not null continue
//   displaying the content and move to the
//   next node till the temp becomes head
if(temp != NULL) {
cout<<"The list contains: ";
while(true) {
cout<<temp->data<<" ";
temp = temp->next;
break;
}
cout<<"\n";
} else {

//3. If the temp node is null at the start,
//   the list is empty
cout<<"The list is empty.\n";
}
}
```
```void PrintList(struct Node* head_ref) {

//1. create a temp node pointing to head

//2. if the temp node is not null continue
//   displaying the content and move to the
//   next node till the temp becomes head
printf("The list contains: ");
while (1) {
printf("%i ",temp->data);
temp = temp->next;
break;
}
printf("\n");
} else {

//3. If the temp node is null at the start,
//   the list is empty
printf("The list is empty.\n");
}
}
```
```def PrintList(self):

#1. create a temp node pointing to head

#2. if the temp node is not null continue
#   displaying the content and move to the
#   next node till the temp becomes head
if(temp != None):
print("The list contains:", end=" ")
while (True):
print(temp.data, end=" ")
temp = temp.next
break
print()
else:

#3. If the temp node is null at the start,
#   the list is empty
print("The list is empty.")
```
```void PrintList() {

//1. create a temp node pointing to head
Node temp = new Node();

//2. if the temp node is not null continue
//   displaying the content and move to the
//   next node till the temp becomes head
if(temp != null) {
System.out.print("The list contains: ");
while(true) {
System.out.print(temp.data + " ");
temp = temp.next;
break;
}
System.out.print();
} else {

//3. If the temp node is null at the start,
//   the list is empty
System.out.println("The list is empty.");
}
}
```
```public void PrintList() {

//1. create a temp node pointing to head
Node temp = new Node();

//2. if the temp node is not null continue
//   displaying the content and move to the
//   next node till the temp becomes head
if(temp != null) {
Console.Write("The list contains: ");
while(true) {
Console.Write(temp.data + " ");
temp = temp.next;
break;
}
Console.WriteLine();
} else {

//3. If the temp node is null at the start,
//   the list is empty
Console.WriteLine("The list is empty.");
}
}
```
```public function PrintList() {

//1. create a temp node pointing to head
\$temp = new Node();

//2. if the temp node is not null continue
//   displaying the content and move to the
//   next node till the temp becomes head
if(\$temp != null) {
echo "The list contains: ";
while(true) {
echo \$temp->data." ";
\$temp = \$temp->next;
break;
}
echo "\n";
} else {

//3. If the temp node is null at the start,
//   the list is empty
echo "The list is empty.\n";
}
}
```

The below is a complete program that uses above discussed concept to traverse through the circular doubly linked list and displaying its content.

```#include <iostream>
using namespace std;

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

private:
public:
}

//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;
} else {
temp = temp->next;
temp->next = newNode;
newNode->prev = temp;
}
}

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

// test the code
int main() {

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

//traverse to display the content of the list.
MyList.PrintList();

return 0;
}
```

The above code will give the following output:

```The list contains: 10 20 30
```
```#include <stdio.h>
#include <stdlib.h>

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

//Add new element at the end of the list
void push_back(struct Node** head_ref, int newElement) {
struct Node *newNode, *temp;
newNode = (struct Node*)malloc(sizeof(struct Node));
newNode->data = newElement;
newNode->next = NULL;
newNode->prev = NULL;
} else {
temp = temp->next;
}
temp->next = newNode;
newNode->prev = temp;
}
}

//display the content of the list
printf("The list contains: ");
while (1) {
printf("%i ",temp->data);
temp = temp->next;
break;
}
printf("\n");
} else {
printf("The list is empty.\n");
}
}

// test the code
int main() {
struct Node* MyList = NULL;

//Add three elements at the end of the list.
push_back(&MyList, 10);
push_back(&MyList, 20);
push_back(&MyList, 30);

//traverse to display the content of the list.
PrintList(MyList);

return 0;
}
```

The above code will give the following output:

```The list contains: 10 20 30
```
```# node structure
class Node:
def __init__(self, data):
self.data = data
self.next = None
self.prev = None

def __init__(self):

#Add new element at the end of the list
def push_back(self, newElement):
newNode = Node(newElement)
return
else:
temp = temp.next
temp.next = newNode
newNode.prev = temp

#display the content of the list
def PrintList(self):
if(temp != None):
print("The list contains:", end=" ")
while (True):
print(temp.data, end=" ")
temp = temp.next
break
print()
else:
print("The list is empty.")

# test the code

#Add three elements at the end of the list.
MyList.push_back(10)
MyList.push_back(20)
MyList.push_back(30)

#traverse to display the content of the list.
MyList.PrintList()
```

The above code will give the following output:

```The list contains: 10 20 30
```
```//node structure
class Node {
int data;
Node next;
Node prev;
};

}

//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.next = null;
} else {
Node temp = new Node();
temp = temp.next;
temp.next = newNode;
newNode.prev = temp;
}
}

//display the content of the list
void PrintList() {
Node temp = new Node();
if(temp != null) {
System.out.print("The list contains: ");
while(true) {
System.out.print(temp.data + " ");
temp = temp.next;
break;
}
System.out.println();
} else {
System.out.println("The list is empty.");
}
}
};

// test the code
public class Implementation {
public static void main(String[] args) {

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

//traverse to display the content of the list.
MyList.PrintList();
}
}
```

The above code will give the following output:

```The list contains: 10 20 30
```
```using System;

//node structure
class Node {
public int data;
public Node next;
public Node prev;
};

}

//Add new element at the end of the list
public void push_back(int newElement) {
Node newNode = new Node();
newNode.data = newElement;
newNode.next = null;
newNode.prev = null;
} else {
Node temp = new Node();
temp = temp.next;
temp.next = newNode;
newNode.prev = temp;
}
}

//display the content of the list
public void PrintList() {
Node temp = new Node();
if(temp != null) {
Console.Write("The list contains: ");
while(true) {
Console.Write(temp.data + " ");
temp = temp.next;
break;
}
Console.WriteLine();
} else {
Console.WriteLine("The list is empty.");
}
}
};

// test the code
class Implementation {
static void Main(string[] args) {

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

//traverse to display the content of the list.
MyList.PrintList();
}
}
```

The above code will give the following output:

```The list contains: 10 20 30
```
```<?php
//node structure
class Node {
public \$data;
public \$next;
public \$prev;
}

public function __construct(){
}

//Add new element at the end of the list
public function push_back(\$newElement) {
\$newNode = new Node();
\$newNode->data = \$newElement;
\$newNode->next = null;
\$newNode->prev = null;
} else {
\$temp = new Node();
\$temp = \$temp->next;
}
\$temp->next = \$newNode;
\$newNode->prev = \$temp;
}
}

//display the content of the list
public function PrintList() {
\$temp = new Node();
if(\$temp != null) {
echo "The list contains: ";
while(true) {
echo \$temp->data." ";
\$temp = \$temp->next;
break;
}
echo "\n";
} else {
echo "The list is empty.\n";
}
}
};

// test the code

//Add three elements at the end of the list.
\$MyList->push_back(10);
\$MyList->push_back(20);
\$MyList->push_back(30);

//traverse to display the content of the list.
\$MyList->PrintList();
?>
```

The above code will give the following output:

```The list contains: 10 20 30
```

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