Data Structures - Doubly Linked List Other Related Topics
Data Structures - Doubly Linked List Other Related Topics

Doubly Linked List - Traversal

Traversing through a 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 becomes null. If the temp node is empty at the start, then the list contains no item.

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

void PrintList() {
  
  //1. create a temp node pointing to head
  Node* temp = head;
  
  //2. if the temp node is not null continue 
  //   displaying the content and move to the
  //   next node till the temp becomes null
  if(temp != NULL) {
    cout<<"The list contains: ";
    while(temp != NULL) {
      cout<<temp->data<<" ";
      temp = temp->next;
    }
    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
  struct Node* temp = head_ref;
  
  //2. if the temp node is not null continue 
  //   displaying the content and move to the 
  //   next node till the temp becomes null
  if(head_ref != NULL) {
    printf("The list contains: ");
    while (temp != NULL) {
      printf("%i ",temp->data);
      temp = temp->next;    
    }
    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
  temp = self.head
  
  #2. if the temp node is not null continue 
  #   displaying the content and move to the 
  #   next ode till the temp becomes null
  if(temp != None):
    print("The list contains:", end=" ")
    while (temp != None):
      print(temp.data, end=" ")
      temp = temp.next
    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();
  temp = this.head;

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

  //2. if the temp node is not null continue 
  //   displaying the content and move to the 
  //   next node till the temp becomes null
  if(temp != null) {
    Console.Write("The list contains: ");
    while(temp != null) {
      Console.Write(temp.data + " ");
      temp = temp.next;
    }
    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();
  $temp = $this->head;
  
  //2. if the temp node is not null continue 
  //   displaying the content and move to the 
  //   next node till the temp becomes null
  if($temp != null) {
    echo "The list contains: ";
    while($temp != null) {
      echo $temp->data." ";
      $temp = $temp->next;
    }
    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 doubly linked list and displaying its content.

#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;
      } else {
        Node* temp = head;
        while(temp->next != NULL)
          temp = temp->next;
        temp->next = newNode;
        newNode->prev = temp;
      }    
    }

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

  //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;
  if(*head_ref == NULL) {
    *head_ref = newNode;
  } else {
    temp = *head_ref;
    while(temp->next != NULL) {
      temp = temp->next;
    }    
    temp->next = newNode;
    newNode->prev = temp;
  }
}

//display the content of the list
void PrintList(struct Node* head_ref) {
  struct Node* temp = head_ref;
  if(head_ref != NULL) {
    printf("The list contains: ");
    while (temp != NULL) {
      printf("%i ",temp->data);
      temp = temp->next;  
    }
    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

#class Linked List
class LinkedList:
  def __init__(self):
    self.head = None

  #Add new element at the end of the list
  def push_back(self, newElement):
    newNode = Node(newElement)
    if(self.head == None):
      self.head = newNode
      return
    else:
      temp = self.head
      while(temp.next != None):
        temp = temp.next
      temp.next = newNode
      newNode.prev = temp

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

# test the code                  
MyList = LinkedList()

#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;
};

class LinkedList {
  Node head;

  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;
    } else {
      Node temp = new Node();
      temp = head;
      while(temp.next != null)
        temp = temp.next;
      temp.next = newNode;
      newNode.prev = temp;
    }    
  }

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

// test the code 
public class Implementation {
  public static void main(String[] args) {
    LinkedList MyList = new LinkedList();

    //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;
};

class LinkedList {
  Node head;

  public LinkedList(){
    head = null;
  }
  
  //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;
    if(head == null) {
      head = newNode;
    } else {
      Node temp = new Node();
      temp = head;
      while(temp.next != null)
        temp = temp.next;
      temp.next = newNode;
      newNode.prev = temp;
    }    
  }

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

// test the code
class Implementation {  
  static void Main(string[] args) {
    LinkedList MyList = new LinkedList();

    //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;
}

class LinkedList {
  public $head;

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

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

// test the code  
$MyList = new LinkedList();

//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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