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

Doubly Linked List - Count nodes

Counting nodes in a doubly linked list is very useful while working on it. It requires creating a temp node pointing to the head of the list and a variable called i with initial value 0. If the temp node is not null, increase i by 1 and move to the next node using temp next. Repeat the process till the temp node becomes null. The final value of i will be the total number of nodes in the doubly linked list.

The function countNodes is created for this purpose. It is a 4-step process.

int countNodes() {
  
  //1. create a temp node pointing to head
  Node* temp = head;

  //2. create a variable to count nodes
  int i = 0;
  
  //3. if the temp node is not null increase 
  //   i by 1 and move to the next node, repeat
  //   the process till the temp becomes null
  while(temp != NULL) {
    i++;
    temp = temp->next;
  }

  //4. return the count
  return i;  
} 

int countNodes(struct Node* head_ref) {
  
  //1. create a temp node pointing to head
  struct Node* temp = head_ref;
  
  //2. create a variable to count nodes
  int i = 0;

  //3. if the temp node is not null increase 
  //   i by 1 and move to the next node, repeat
  //   the process till the temp becomes null
  while (temp != NULL) {
    i++;
    temp = temp->next;    
  }
  
  //4. return the count
  return i;    
}

def countNodes(self):
  
  #1. create a temp node pointing to head
  temp = self.head
  
  #2. create a variable to count nodes
  i = 0

  #3. if the temp node is not null increase 
  #   i by 1 and move to the next node, repeat
  #   the process till the temp becomes null
  while (temp != None):
    i += 1
    temp = temp.next

  #4. return the count
  return i    

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

  //2. create a variable to count nodes
  int i = 0;

  //3. if the temp node is not null increase 
  //   i by 1 and move to the next node, repeat
  //   the process till the temp becomes null
  while(temp != null) {
    i++;
    temp = temp.next;
  }

  //4. return the count
  return i;  
}      

public int countNodes() {
  
  //1. create a temp node pointing to head
  Node temp = new Node();
  temp = this.head;

  //2. create a variable to count nodes
  int i = 0;

  //3. if the temp node is not null increase 
  //   i by 1 and move to the next node, repeat
  //   the process till the temp becomes null
  while(temp != null) {
    i++;
    temp = temp.next;
  }

  //4. return the count
  return i;  
} 

public function countNodes() {
  
  //1. create a temp node pointing to head
  $temp = new Node();
  $temp = $this->head;
  
  //2. create a variable to count nodes
  $i = 0;

  //3. if the temp node is not null increase 
  //   i by 1 and move to the next node, repeat
  //   the process till the temp becomes null
  while($temp != null) {
    $i++;
    $temp = $temp->next;
  }

  //4. return the count
  return $i;  
}

The below is a complete program that uses above discussed concept of counting the total number of nodes of a doubly linked list.

#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;
      }    
    }

    //count nodes in the list
    int countNodes() {
      Node* temp = head;
      int i = 0;
      while(temp != NULL) {
        i++;
        temp = temp->next;
      }
      return i;  
    } 

    //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 four elements in the list.
  MyList.push_back(10);
  MyList.push_back(20);
  MyList.push_back(30);
  MyList.push_back(40);

  //Display the content of the list.
  MyList.PrintList();

  //number of nodes in the list
  cout<<"No. of nodes: "<<MyList.countNodes();
  
  return 0; 
}

The above code will give the following output: 

The list contains: 10 20 30 40
No. of nodes: 4

#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;
  }
}

//count nodes in the list
int countNodes(struct Node* head_ref) {
  struct Node* temp = head_ref;
  int i = 0;
  while (temp != NULL) {
    i++;
    temp = temp->next;    
  }
  return i;    
}

//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 four elements in the list.
  push_back(&MyList, 10);
  push_back(&MyList, 20);
  push_back(&MyList, 30);
  push_back(&MyList, 40);

  //Display the content of the list.
  PrintList(MyList);

  //number of nodes in the list
  printf("No. of nodes: %i",countNodes(MyList));
  return 0; 
}

The above code will give the following output: 

The list contains: 10 20 30 40
No. of nodes: 4

# 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

  #count nodes in the list
  def countNodes(self):
    temp = self.head
    i = 0
    while (temp != None):
      i += 1
      temp = temp.next
    return i 

  #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 four elements in the list.
MyList.push_back(10)
MyList.push_back(20)
MyList.push_back(30)
MyList.push_back(40)

#Display the content of the list.
MyList.PrintList()

#number of nodes in the list
print("No. of nodes: ", MyList.countNodes())

The above code will give the following output: 

The list contains: 10 20 30 40
No. of nodes: 4

//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;
    }    
  }

  //count nodes in the list
  int countNodes() {
    Node temp = new Node();
    temp = this.head;
    int i = 0;
    while(temp != null) {
      i++;
      temp = temp.next;
    }
    return i;  
  }  

  //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 four elements in the list.
    MyList.push_back(10);
    MyList.push_back(20);
    MyList.push_back(30);
    MyList.push_back(40);

    //Display the content of the list.
    MyList.PrintList();

    //number of nodes in the list
    System.out.print("No. of nodes: "+ MyList.countNodes()); 
  }
}

The above code will give the following output: 

The list contains: 10 20 30 40
No. of nodes: 4

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;
    }    
  }

  //count nodes in the list
  public int countNodes() {
    Node temp = new Node();
    temp = this.head;
    int i = 0;
    while(temp != null) {
      i++;
      temp = temp.next;
    }
   return i;  
  }  

  //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 four elements in the list.
    MyList.push_back(10);
    MyList.push_back(20);
    MyList.push_back(30);
    MyList.push_back(40);

    //Display the content of the list.
    MyList.PrintList();  

    //number of nodes in the list
    Console.Write("No. of nodes: "+ MyList.countNodes());   
  }
}

The above code will give the following output: 

The list contains: 10 20 30 40
No. of nodes: 4

<?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;
    }    
  }

  //count nodes in the list
  public function countNodes() {
    $temp = new Node();
    $temp = $this->head;
    $i = 0;
    while($temp != null) {
      $i++;
      $temp = $temp->next;
    }
    return $i;  
  }  

  //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 four elements in the list.
$MyList->push_back(10);
$MyList->push_back(20);
$MyList->push_back(30);
$MyList->push_back(40);

//Display the content of the list.
$MyList->PrintList();

//number of nodes in the list
echo "No. of nodes: ".$MyList->countNodes();
?>

The above code will give the following output: 

The list contains: 10 20 30 40
No. of nodes: 4
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