Data Structures - Circular Doubly Linked List Other Related Topics
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Circular Doubly Linked List - Delete all nodes



Deleting all nodes of a circular doubly linked list requires traverse through the list and deleting each node one by one. It requires creating a current node pointing to the next of head. Delete the current node and move to the next node using temp node. Repeat the process till the current node becomes head. At last, delete the head.

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

void deleteAllNodes() {
  if(head != NULL) {
    
    //1. if head is not null create a temp node
    //   and current node pointed to next of head
    Node *temp, *current;
    current = head->next;
    
    //2. if current node is not equal to head, delete the
    //   current node and move current to next node using temp,
    //   repeat the process till the current reaches the head
    while(current != head) {
      temp = current->next;
      free(current);
      current = temp;
    }

    //3. Delete the head
    free(head);
    head = NULL;
  }
  cout<<"All nodes are deleted successfully.\n";  
}
void deleteAllNodes(struct Node** head_ref) {
  if(*head_ref != NULL) {
    
    //1. if head is not null create a temp node
    //   and current node pointed to next of head
    struct Node *temp, *current;
    current = (*head_ref)->next;
    
    //2. if current node is not equal to head, delete the
    //   current node and move current to next node using temp,
    //   repeat the process till the current reaches the head
    while(current != *head_ref) {
      temp = current->next;
      free(current);
      current = temp;
    }

    //3. Delete the head
    free(*head_ref);
    *head_ref = NULL;
  }
  printf("All nodes are deleted successfully.\n");  
}
def deleteAllNodes(self):
  if self.head != None:
    
    #1. if head is not null create a temp node
    #   and current node pointed to next of head
    current = self.head.next
    while(current != self.head):
      
      #2. if current node is not equal to head, delete the
      #   current node and move current to next node using temp,
      #   repeat the process till the current reaches the head
      temp = current.next
      current = None
      current = temp
    
    #3. Delete the head
    self.head = None

  print("All nodes are deleted successfully.") 
void deleteAllNodes() {
  if(this.head != null) {
    
    //1. if head is not null create a temp node
    //   and current node pointed to next of head
    Node temp = new Node();
    Node current = new Node();
    current = this.head.next;
    
    //2. if current node is not equal to head, delete the
    //   current node and move current to next node using temp,
    //   repeat the process till the current reaches the head
    while(current != this.head) {
      temp = current.next;
      current = null;
      current = temp;
    }

    //3. Delete the head
    this.head = null;
  }
  System.out.println("All nodes are deleted successfully.");
}
public void deleteAllNodes() {
  if(this.head != null) {
    
    //1. if head is not null create a temp node
    //   and current node pointed to next of head
    Node temp = new Node();
    Node current = new Node();
    current = this.head.next;
    
    //2. if current node is not equal to head, delete the
    //   current node and move current to next node using temp,
    //   repeat the process till the current reaches the head
    while(current != this.head) {
      temp = current.next;
      current = null;
      current = temp;
    }

    //3. Delete the head
    this.head = null;
  }
  Console.WriteLine("All nodes are deleted successfully."); 
}
public function deleteAllNodes() {
  if($this->head != null) {
    
    //1. if head is not null create a temp node
    //   and current node pointed to next of head
    $temp = new Node();
    $current = new Node();
    $current = $this->head->next;
    
    //2. if current node is not equal to head, delete the
    //   current node and move current to next node using temp,
    //   repeat the process till the current reaches the head
    while($current != $this->head) {
      $temp = $current->next;
      $current = null;
      $current = $temp;
    }

    //3. Delete the head
    $this->head = null;
  }
  echo "All nodes are deleted successfully.\n";  
}

The below is a complete program that uses above discussed concept of deleting all nodes of a circular doubly linked list which makes the list empty with size zero.

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

    //delete all nodes of the list
    void deleteAllNodes() {
      if(head != NULL) {
        Node *temp, *current;
        current = head->next;
        while(current != head) {
          temp = current->next;
          free(current);
          current = temp;
        }
        free(head);
        head = NULL;
      }
      cout<<"All nodes are deleted successfully.\n";  
    }

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

  //delete all nodes of the list
  MyList.deleteAllNodes();

  //Display the content of the list.
  MyList.PrintList();
  
  return 0; 
}

The above code will give the following output:

The list contains: 10 20 30 40 
All nodes are deleted successfully.
The list is empty.
#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;
     newNode->next = *head_ref;
     newNode->prev = *head_ref;
  } else {
    temp = *head_ref;
    while(temp->next != *head_ref) {
      temp = temp->next;
    }    
    temp->next = newNode;
    newNode->next = *head_ref;
    newNode->prev = temp;
    (*head_ref)->prev = newNode;
  }
}

//delete all nodes of the list
void deleteAllNodes(struct Node** head_ref) {
  if(*head_ref != NULL) {
    struct Node *temp, *current;
    current = (*head_ref)->next;
    while(current != *head_ref) {
      temp = current->next;
      free(current);
      current = temp;
    }
    free(*head_ref);
    *head_ref = NULL;
  }
  printf("All nodes are deleted successfully.\n");  
}

//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 (1) {
      printf("%i ",temp->data);
      temp = temp->next;
      if(temp == head_ref)
        break;    
    }
    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);

  //delete all nodes of the list
  deleteAllNodes(&MyList);

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

  return 0; 
}

The above code will give the following output:

The list contains: 10 20 30 40 
All nodes are deleted successfully.
The list is empty.
# 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
      newNode.next = self.head
      newNode.prev = self.head
      return
    else:
      temp = self.head
      while(temp.next != self.head):
        temp = temp.next
      temp.next = newNode
      newNode.next = self.head
      newNode.prev = temp
      self.head.prev = newNode

  #delete all nodes of the list
  def deleteAllNodes(self):
    if self.head != None:
      current = self.head.next
      while(current != self.head):
        temp = current.next
        current = None
        current = temp
      self.head = None
    print("All nodes are deleted successfully.") 

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

#delete all nodes of the list
MyList.deleteAllNodes()

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

The above code will give the following output:

The list contains: 10 20 30 40 
All nodes are deleted successfully.
The list is empty.
//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.next = null;
    if(head == null) {
      head = newNode;
      newNode.next = head;
      newNode.prev = head;
    } else {
      Node temp = new Node();
      temp = head;
      while(temp.next != head)
        temp = temp.next;
      temp.next = newNode;
      newNode.next = head;
      newNode.prev = temp;
      head.prev = newNode;
    }    
  }

  //delete all nodes of the list
  void deleteAllNodes() {
    if(this.head != null) {
      Node temp = new Node();
      Node current = new Node();
      current = this.head.next;
      while(current != this.head) {
        temp = current.next;
        current = null;
        current = temp;
      }
      this.head = null;
    }
    System.out.println("All nodes are deleted successfully.");
  }

  //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(true) {
        System.out.print(temp.data + " ");
        temp = temp.next;
        if(temp == this.head)
          break;
      }
      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();

    //delete all nodes of the list
    MyList.deleteAllNodes();

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

The above code will give the following output:

The list contains: 10 20 30 40 
All nodes are deleted successfully.
The list is empty.
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;
      newNode.next = head;
      newNode.prev = head;
    } else {
      Node temp = new Node();
      temp = head;
      while(temp.next != head)
        temp = temp.next;
      temp.next = newNode;
      newNode.next = head;
      newNode.prev = temp;
      head.prev = newNode;
    }    
  }

  //delete all nodes of the list
  public void deleteAllNodes() {
    if(this.head != null) {
      Node temp = new Node();
      Node current = new Node();
      current = this.head.next;
      while(current != this.head) {
        temp = current.next;
        current = null;
        current = temp;
      }
      this.head = null;
    }
    Console.WriteLine("All nodes are deleted successfully."); 
  }

  //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(true) {
        Console.Write(temp.data + " ");
        temp = temp.next;
        if(temp == this.head)
          break;        
      }
      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();  

    //delete all nodes of the list
    MyList.deleteAllNodes();

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

The above code will give the following output:

The list contains: 10 20 30 40 
All nodes are deleted successfully.
The list is empty.
<?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;
      $newNode->next = $this->head;
    } else {
      $temp = new Node();
      $temp = $this->head;
      while($temp->next !== $this->head) {
        $temp = $temp->next;
      }
      $temp->next = $newNode;
      $newNode->next = $this->head;
      $newNode->prev = $temp;
      $this->head->prev = $newNode;
    }    
  }

  //delete all nodes of the list
  public function deleteAllNodes() {
    if($this->head != null) {
      $temp = new Node();
      $current = new Node();
      $current = $this->head->next;
      while($current != $this->head) {
        $temp = $current->next;
        $current = null;
        $current = $temp;
      }
      $this->head = null;
    }
    echo "All nodes are deleted successfully.\n";  
  }

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

//delete all nodes of the list
$MyList->deleteAllNodes();

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

The above code will give the following output:

The list contains: 10 20 30 40 
All nodes are deleted successfully.
The list is empty.

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