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

Circular Doubly Linked List - Delete a node at the given position

In this method, a node at the specified position in the circular doubly linked list is deleted. For example - if the given list is 10->20->30 and the 2nd node is deleted, the list becomes 10->20.

First, create two nodes temp and nodeToDelete to traverse through the list and track the node to delete respectively. After that count the number of elements in the list to check whether the specified position is valid or not (It must lie in the range of [1, n], where n is number of elements in the list). If the specified valid position is 1 and head is the only element in the list, then make the head as null. If the specified valid position is 1 and list contains more than one elements, then make next of head as new head and adjust links accordingly. If the specified valid position is greater than 1 then traverse to the node previous to the given position and delete the given node and adjust links accordingly.

Circular Doubly Linked List - Delete Node

The function pop_at is created for this purpose. It is a 5-step process.

void pop_at(int position) {
  
  //1. create two nodes - temp and nodeToDelete 
  //   to traverse and track the node to delete  
  Node* nodeToDelete = head; 
  Node* temp = head;
  int NoOfElements = 0;

  //2. Find the number of elements in the list
  if(temp != NULL) {
    NoOfElements++;
    temp = temp->next;
  }
  while(temp != head) {
    NoOfElements++;
    temp = temp->next;
  }

  //3. check if the specified position is valid
  if(position < 1 || position > NoOfElements) {
    cout<<"\nInavalid position.";
  } else if (position == 1) {
  
  //4. if the position is 1 and head is the only element
  //   in the list, then make it null, else make next
  //   of head as new head and adjust links accordingly
    if(head->next == head) {
      head = NULL;
    } else {     
      while(temp->next != head)
        temp = temp->next;
      head = head->next;
      temp->next = head; 
      head->prev = temp;
      free(nodeToDelete); 
    }
  } else {

   //5. Else, traverse to the node previous to
   //   the given position and delete the given 
   //   node and adjust links accordingly 
    temp = head;
    for(int i = 1; i < position-1; i++)
      temp = temp->next;
    nodeToDelete = temp->next;
    temp->next = temp->next->next;
    temp->next->prev = temp;
    free(nodeToDelete); 
  }
}

void pop_at(struct Node** head_ref, int position) {  
  
  //1. create two nodes - temp and nodeToDelete 
  //   to traverse and track the node to delete  
  struct Node *nodeToDelete = *head_ref;
  struct Node *temp = *head_ref;
  int NoOfElements = 0;

  //2. Find the number of elements in the list
  if(temp != NULL) {
    NoOfElements++;
    temp = temp->next;
  }
  while(temp != *head_ref) {
    NoOfElements++;
    temp = temp->next;
  }

  //3. check if the specified position is valid
  if(position < 1 || position > NoOfElements) {
    printf("\nInavalid position.");
  } else if (position == 1) {
  
  //4. if the position is 1 and head is the only element
  //   in the list, then make it null, else make next
  //   of head as new head and adjust links accordingly
    if((*head_ref)->next == *head_ref) {
      *head_ref = NULL;
    } else {
      while(temp->next != *head_ref)
        temp = temp->next;
      *head_ref = (*head_ref)->next;
      temp->next = *head_ref; 
      (*head_ref)->prev = temp;
      free(nodeToDelete);
    }
  } else {

   //5. Else, traverse to the node previous to
   //   the given position and delete the given 
   //   node and adjust links accordingly 
    temp = *head_ref;
    for(int i = 1; i < position-1; i++) 
      temp = temp->next;
    nodeToDelete = temp->next;
    temp->next = temp->next->next;
    temp->next->prev = temp;
    free(nodeToDelete);  
  }
}     

def pop_at(self, position):     

  #1. create two nodes - temp and nodeToDelete 
  #   to traverse and track the node to delete  
  nodeToDelete = self.head
  temp = self.head
  NoOfElements = 0

  #2. Find the number of elements in the list
  if(temp != None):
    NoOfElements += 1
    temp = temp.next
  while(temp != self.head):
    NoOfElements += 1
    temp = temp.next

  #3. check if the specified position is valid
  if(position < 1 or position > NoOfElements):
    print("\nInavalid position.")
  elif (position == 1):
  
  #4. if the position is 1 and head is the only element
  #   in the list, then make it null, else make next
  #   of head as new head and adjust links accordingly
    if(self.head.next == self.head):
      self.head = None
    else:
      while(temp.next != self.head):
        temp = temp.next
      self.head = self.head.next
      temp.next = self.head
      self.head.prev = temp
      nodeToDelete = None

  else:

   #5. Else, traverse to the node previous to
   #   the given position and delete the given 
   #   node and adjust links accordingly 
    temp = self.head
    for i in range(1, position-1):
      temp = temp.next 
    nodeToDelete = temp.next
    temp.next = temp.next.next
    temp.next.prev = temp
    nodeToDelete = None

void pop_at(int position) { 
  
  //1. create two nodes - temp and nodeToDelete 
  //   to traverse and track the node to delete  
  Node nodeToDelete = head;
  Node temp = head;
  int NoOfElements = 0;

  //2. Find the number of elements in the list
  if(temp != null) {
    NoOfElements++;
    temp = temp.next;
  }
  while(temp != head) {
    NoOfElements++;
    temp = temp.next;
  }

  //3. check if the specified position is valid
  if(position < 1 || position > NoOfElements) {
    System.out.print("\nInvalid position.");
  } else if (position == 1) {
  
  //4. if the position is 1 and head is the only element
  //   in the list, then make it null, else make next
  //   of head as new head and adjust links accordingly
    if(head.next == head) {
      head = null;
    } else {
      while(temp.next != head)
        temp = temp.next;
      head = head.next;
      temp.next = head; 
      head.prev = temp;
      nodeToDelete = null; 
    }
  } else {

   //5. Else, traverse to the node previous to
   //   the given position and delete the given 
   //   node and adjust links accordingly 
    temp = head;
    for(int i = 1; i < position-1; i++)
      temp = temp.next;
    nodeToDelete = temp.next;
    temp.next = temp.next.next;
    temp.next.prev = temp;
    nodeToDelete = null;   
  }
}

public void pop_at(int position) { 
  
  //1. create two nodes - temp and nodeToDelete 
  //   to traverse and track the node to delete  
  Node nodeToDelete = head;
  Node temp = head;
  int NoOfElements = 0;

  //2. Find the number of elements in the list
  if(temp != null) {
    NoOfElements++;
    temp = temp.next;
  }
  while(temp != head) {
    NoOfElements++;
    temp = temp.next;
  }

  //3. check if the specified position is valid
  if(position < 1 || position > NoOfElements) {
    Console.Write("\nInvalid position.");
  } else if (position == 1) {
  
  //4. if the position is 1 and head is the only element
  //   in the list, then make it null, else make next
  //   of head as new head and adjust links accordingly
    if(head.next == head) {
      head = null;
    } else {
      while(temp.next != head)
        temp = temp.next;
      head = head.next;
      temp.next = head;
      head.prev = temp; 
      nodeToDelete = null; 
    }
  } else {

   //5. Else, traverse to the node previous to
   //   the given position and delete the given 
   //   node and adjust links accordingly 
    temp = head;
    for(int i = 1; i < position-1; i++) 
      temp = temp.next;
    nodeToDelete = temp.next;
    temp.next = temp.next.next;
    temp.next.prev = temp;
    nodeToDelete = null;   
  }
}

public function pop_at($position) {     

  //1. create two nodes - temp and nodeToDelete 
  //   to traverse and track the node to delete  
  $nodeToDelete = $this->head;
  $temp = $this->head;
  $NoOfElements = 0;

  //2. Find the number of elements in the list
  if($temp != null) {
    $NoOfElements++;
    $temp = $temp->next;
  }
  while($temp != $this->head) {
    $NoOfElements++;
    $temp = $temp->next;
  }

  //3. check if the specified position is valid
  if($position < 1 || $position > $NoOfElements) {
    echo "\nInvalid position.";
  } else if ($position == 1) {
  
  //4. if the position is 1 and head is the only element
  //   in the list, then make it null, else make next
  //   of head as new head and adjust links accordingly
    if($this->head->next == $this->head) {
      $this->head = null;
    } else {
      while($temp->next != $this->head)
        $temp = $temp->next;
      $this->head = $this->head->next;
      $temp->next = $this->head; 
      $this->head->prev = $temp;
      $nodeToDelete = null; 
    }
  } else {

   //5. Else, traverse to the node previous to
   //   the given position and delete the given 
   //   node and adjust links accordingly 
    $temp = $this->head;
    for($i = 1; $i < $position-1; $i++) 
      $temp = $temp->next;
    $nodeToDelete = $temp->next;
    $temp->next = $temp->next->next;
    $temp->next->prev = $temp;
    $nodeToDelete = null;  
  }
}

The below is a complete program that uses above discussed concept to delete a node at a given position in the circular 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;
        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 an element at the given position
    void pop_at(int position) {
      Node* nodeToDelete = head; 
      Node* temp = head;
      int NoOfElements = 0;

      if(temp != NULL) {
        NoOfElements++;
        temp = temp->next;
      }
      while(temp != head) {
        NoOfElements++;
        temp = temp->next;
      }

      if(position < 1 || position > NoOfElements) {
        cout<<"\nInavalid position.";
      } else if (position == 1) {
        if(head->next == head) {
          head = NULL;
        } else {     
          while(temp->next != head)
            temp = temp->next;
          head = head->next;
          temp->next = head; 
          head->prev = temp;
          free(nodeToDelete); 
        }
      } else {
        temp = head;
        for(int i = 1; i < position-1; i++)
          temp = temp->next;
        nodeToDelete = temp->next;
        temp->next = temp->next->next;
        temp->next->prev = temp;
        free(nodeToDelete); 
      }
    }

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

  //Delete an element at position 2
  MyList.pop_at(2);
  MyList.PrintList();

  //Delete an element at position 1
  MyList.pop_at(1);  
  MyList.PrintList();  

  return 0; 
}

The above code will give the following output: 

The list contains: 10 20 30
The list contains: 10 30
The list contains: 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;
     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 an element at the given position
void pop_at(struct Node** head_ref, int position) {  
  struct Node *nodeToDelete = *head_ref;
  struct Node *temp = *head_ref;
  int NoOfElements = 0;

  if(temp != NULL) {
    NoOfElements++;
    temp = temp->next;
  }
  while(temp != *head_ref) {
    NoOfElements++;
    temp = temp->next;
  }

  if(position < 1 || position > NoOfElements) {
    printf("\nInavalid position.");
  } else if (position == 1) {
  
    if((*head_ref)->next == *head_ref) {
      *head_ref = NULL;
    } else {
      while(temp->next != *head_ref)
        temp = temp->next;
      *head_ref = (*head_ref)->next;
      temp->next = *head_ref; 
      (*head_ref)->prev = temp;
      free(nodeToDelete);
    }
  } else {
    temp = *head_ref;
    for(int i = 1; i < position-1; i++) 
      temp = temp->next;
    nodeToDelete = temp->next;
    temp->next = temp->next->next;
    temp->next->prev = temp;
    free(nodeToDelete);  
  }
}  

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

  //Delete an element at position 2
  pop_at(&MyList, 2);
  PrintList(MyList);  

  //Delete an element at position 1
  pop_at(&MyList, 1);
  PrintList(MyList); 

  return 0; 
}

The above code will give the following output: 

The list contains: 10 20 30
The list contains: 10 30
The list contains: 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
      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 an element at the given position
  def pop_at(self, position):     
    nodeToDelete = self.head
    temp = self.head
    NoOfElements = 0

    if(temp != None):
      NoOfElements += 1
      temp = temp.next
    while(temp != self.head):
      NoOfElements += 1
      temp = temp.next

    if(position < 1 or position > NoOfElements):
      print("\nInavalid position.")
    elif (position == 1):
      if(self.head.next == self.head):
        self.head = None
      else:
        while(temp.next != self.head):
          temp = temp.next
        self.head = self.head.next
        temp.next = self.head
        self.head.prev = temp
        nodeToDelete = None

    else:
      temp = self.head
      for i in range(1, position-1):
        temp = temp.next 
      nodeToDelete = temp.next
      temp.next = temp.next.next
      temp.next.prev = temp
      nodeToDelete = None

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

#Delete an element at position 2
MyList.pop_at(2)
MyList.PrintList()

#Delete an element at position 1
MyList.pop_at(1)
MyList.PrintList()

The above code will give the following output: 

The list contains: 10 20 30
The list contains: 10 30
The list contains: 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.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 an element at the given position
  void pop_at(int position) { 
    Node nodeToDelete = head;
    Node temp = head;
    int NoOfElements = 0;

    if(temp != null) {
      NoOfElements++;
      temp = temp.next;
    }
    while(temp != head) {
      NoOfElements++;
      temp = temp.next;
    }

    if(position < 1 || position > NoOfElements) {
      System.out.print("\nInvalid position.");
    } else if (position == 1) {
      if(head.next == head) {
        head = null;
      } else {
        while(temp.next != head)
          temp = temp.next;
        head = head.next;
        temp.next = head; 
        head.prev = temp;
        nodeToDelete = null; 
      }
    } else {
      temp = head;
      for(int i = 1; i < position-1; i++)
        temp = temp.next;
      nodeToDelete = temp.next;
      temp.next = temp.next.next;
      temp.next.prev = temp;
      nodeToDelete = null;   
    }
  }

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

    //Delete an element at position 2
    MyList.pop_at(2);
    MyList.PrintList();

    //Delete an element at position 1
    MyList.pop_at(1);
    MyList.PrintList();  
  }
}

The above code will give the following output: 

The list contains: 10 20 30
The list contains: 10 30
The list contains: 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;
      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 an element at the given position
  public void pop_at(int position) { 
    Node nodeToDelete = head;
    Node temp = head;
    int NoOfElements = 0;

    if(temp != null) {
      NoOfElements++;
      temp = temp.next;
    }
    while(temp != head) {
      NoOfElements++;
      temp = temp.next;
    }

    if(position < 1 || position > NoOfElements) {
      Console.Write("\nInvalid position.");
    } else if (position == 1) {
    
      if(head.next == head) {
        head = null;
      } else {
        while(temp.next != head)
          temp = temp.next;
        head = head.next;
        temp.next = head;
        head.prev = temp; 
        nodeToDelete = null; 
      }
    } else {
      temp = head;
      for(int i = 1; i < position-1; i++) 
        temp = temp.next;
      nodeToDelete = temp.next;
      temp.next = temp.next.next;
      temp.next.prev = temp;
      nodeToDelete = null;   
    }
  }

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

    //Delete an element at position 2
    MyList.pop_at(2);
    MyList.PrintList();

    //Delete an element at position 1
    MyList.pop_at(1);
    MyList.PrintList(); 
  }
}

The above code will give the following output: 

The list contains: 10 20 30
The list contains: 10 30
The list contains: 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;
      $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 an element at the given position
  public function pop_at($position) {     
    $nodeToDelete = $this->head;
    $temp = $this->head;
    $NoOfElements = 0;

    if($temp != null) {
      $NoOfElements++;
      $temp = $temp->next;
    }
    while($temp != $this->head) {
      $NoOfElements++;
      $temp = $temp->next;
    }

    if($position < 1 || $position > $NoOfElements) {
      echo "\nInvalid position.";
    } else if ($position == 1) {
      if($this->head->next == $this->head) {
        $this->head = null;
      } else {
        while($temp->next != $this->head)
          $temp = $temp->next;
        $this->head = $this->head->next;
        $temp->next = $this->head; 
        $this->head->prev = $temp;
        $nodeToDelete = null; 
      }
    } else {
      $temp = $this->head;
      for($i = 1; $i < $position-1; $i++) 
        $temp = $temp->next;
      $nodeToDelete = $temp->next;
      $temp->next = $temp->next->next;
      $temp->next->prev = $temp;
      $nodeToDelete = null;  
    }
  } 

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

//Delete an element at position 2
$MyList->pop_at(2);
$MyList->PrintList();

//Delete an element at position 1
$MyList->pop_at(1);
$MyList->PrintList(); 
?>

The above code will give the following output: 

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