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

Doubly Linked List - Delete a node at the given position

In this method, a node at the specified position in the 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, the specified position must be greater than equal to 1. If the specified position is 1 and head is not null, then make the head next as head and delete the previous head. Else, traverse to the node that is previous to the specified position. If the specified node and previous to the specified node are not null then adjust the link. In other case, the specified node will be already null. The below figure describes the process, if the deletion node is other than the head node.

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. check if the position is > 0
  if(position < 1) {
    cout<<"\nposition should be >= 1.";
  } else if (position == 1 && head != NULL) {
      
    //2. if the position is 1 and head is not null, make
    //   head next as head and delete previous head 
    Node* nodeToDelete = head;
    head = head->next;
    free(nodeToDelete);
    if(head != NULL)
      head->prev = NULL;
  } else {
    
    //3. Else, make a temp node and traverse to the 
    //   node previous to the position
    Node* temp = head;
    for(int i = 1; i < position-1; i++) {
      if(temp != NULL) {
        temp = temp->next;
      }
    }
 
    //4. If the previous node and next of the previous  
    //   is not null, adjust links 
    if(temp != NULL && temp->next != NULL) {
        Node* nodeToDelete = temp->next;
        temp->next = temp->next->next;
        if(temp->next->next != NULL)
          temp->next->next->prev = temp->next;  
        free(nodeToDelete); 
    } else {

      //5. Else the given node will be empty.
      cout<<"\nThe node is already null.";
    }       
  }
} 

void pop_at(struct Node** head_ref, int position) {     
  
  //1. check if the position is > 0
  if(position < 1) {
    printf("\nposition should be >= 1.");
  } else if (position == 1 && *head_ref != NULL) {
    
    //2. if the position is 1 and head is not null, make
    //   head next as head and delete previous head  
    struct Node* nodeToDelete = *head_ref;
    *head_ref = (*head_ref)->next;
    free(nodeToDelete);
    if(*head_ref != NULL)
      (*head_ref)->prev = NULL;
  } else {

    //3. Else, make a temp node and traverse to the 
    //   node previous to the position
    struct Node *temp;
    temp = *head_ref;
    for(int i = 1; i < position-1; i++) {
      if(temp != NULL) {
        temp = temp->next;
      }
    }
 
    //4. If the previous node and next of the previous  
    //   is not null, adjust links 
    if(temp != NULL && temp->next != NULL) {
      struct Node* nodeToDelete = temp->next;
      temp->next = temp->next->next; 
      if(temp->next->next != NULL)
        temp->next->next->prev = temp->next;   
      free(nodeToDelete); 
    } else {
      
      //5. Else the given node will be empty.
      printf("\nThe node is already null.");
    }       
  }
}      

def pop_at(self, position):     
  
  #1. check if the position is > 0
  if(position < 1):
    print("\nposition should be >= 1.")
  elif (position == 1 and self.head != None):
    
    #2. if the position is 1 and head is not null, make
    #   head next as head and delete previous head 
    nodeToDelete = self.head
    self.head = self.head.next
    nodeToDelete = None
    if (self.head != None):
      self.head.prev = None
  else:    
    
    #3. Else, make a temp node and traverse to the 
    #   node previous to the position
    temp = self.head
    for i in range(1, position-1):
      if(temp != None):
        temp = temp.next   
    
    #4. If the previous node and next of the previous  
    #   is not null, adjust links 
    if(temp != None and temp.next != None):
      nodeToDelete = temp.next
      temp.next = temp.next.next
      if(temp.next.next != None):
        temp.next.next.prev = temp.next  
      nodeToDelete = None 
    else:
      
      #5. Else the given node will be empty.
      print("\nThe node is already null.")

void pop_at(int position) {     
  
  //1. check if the position is > 0
  if(position < 1) {
    System.out.print("\nposition should be >= 1.");
  } else if (position == 1 && head != null) {
    
    //2. if the position is 1 and head is not null, make
    //   head next as head and delete previous head  
    Node nodeToDelete = head;
    head = head.next;
    nodeToDelete = null;
    if (head != null)
      head.prev = null;
  } else {
    
    //3. Else, make a temp node and traverse to the 
    //   node previous to the position
    Node temp = new Node();
    temp = head;
    for(int i = 1; i < position-1; i++) {
      if(temp != null) {
        temp = temp.next;
      }
    }
 
    //4. If the previous node and next of the previous  
    //   is not null, adjust links 
    if(temp != null && temp.next != null) {
      Node nodeToDelete = temp.next;
      temp.next = temp.next.next; 
      if(temp.next.next != null)
        temp.next.next.prev = temp.next;  
      nodeToDelete = null; 
    } else {
      
      //5. Else the given node will be empty.
      System.out.print("\nThe node is already null.");
    }       
  }
} 

public void pop_at(int position) {     
  
  //1. check if the position is > 0
  if(position < 1) {
    Console.Write("\nposition should be >= 1.");
  } else if (position == 1 && head != null) {
    
    //2. if the position is 1 and head is not null, make
    //   head next as head and delete previous head  
    Node nodeToDelete = head;
    head = head.next;
    nodeToDelete = null;
    if (head != null)
      head.prev = null;
  } else {
    
    //3. Else, make a temp node and traverse to the 
    //   node previous to the position
    Node temp = new Node();
    temp = head;
    for(int i = 1; i < position-1; i++) {
      if(temp != null) {
        temp = temp.next;
      }
    }
 
    //4. If the previous node and next of the previous  
    //   is not null, adjust links 
    if(temp != null && temp.next != null) {
      Node nodeToDelete = temp.next;
      temp.next = temp.next.next; 
      if(temp.next.next != null)
        temp.next.next.prev = temp.next;   
      nodeToDelete = null;  
    } else {
      
      //5. Else the given node will be empty.
      Console.Write("\nThe node is already null.");
    }       
  }
} 

public function pop_at($position) {     
  
  //1. check if the position is > 0
  if($position < 1) {
    echo "\nposition should be >= 1.";
  } else if ($position == 1 && $this->head != null) {
    
    //2. if the position is 1 and head is not null, make
    //   head next as head and delete previous head  
    $nodeToDelete = $this->head;
    $this->head = $this->head->next;
    $nodeToDelete = null;
    if ($this->head != null)
      $this->head->prev = null;
  } else {
    
    //3. Else, make a temp node and traverse to the 
    //   node previous to the position
    $temp = new Node();
    $temp = $this->head;
    for($i = 1; $i < $position-1; $i++) {
      if($temp != null) {
        $temp = $temp->next;
      }
    }
 
    //4. If the previous node and next of the previous  
    //   is not null, adjust links 
    if($temp != null && $temp->next != null) {
      $nodeToDelete = $temp->next;
      $temp->next = $temp->next->next;
      if($temp->next->next != null)
        $temp->next->next->prev = $temp->next;   
      $nodeToDelete = null; 
    } else {
      
      //5. Else the given node will be empty.
      echo "\nThe node is already null.";
    }       
  }
}

The below is a complete program that uses above discussed concept to delete a node at a given position in the 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;
      }    
    }

    //Delete an element at the given position
    void pop_at(int position) {     
      if(position < 1) {
        cout<<"\nposition should be >= 1.";
      } else if (position == 1 && head != NULL) { 
        Node* nodeToDelete = head;
        head = head->next;
        free(nodeToDelete);
        if(head != NULL)
          head->prev = NULL;
      } else {
        Node* temp = head;
        for(int i = 1; i < position-1; i++) {
          if(temp != NULL) {
            temp = temp->next;
          }
        }
        if(temp != NULL && temp->next != NULL) {
          Node* nodeToDelete = temp->next;
          temp->next = temp->next->next;
          if(temp->next->next != NULL)
            temp->next->next->prev = temp->next;  
          free(nodeToDelete); 
        } else {
          cout<<"\nThe node is already null.";
        }       
      }
    } 

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

//Delete an element at the given position
void pop_at(struct Node** head_ref, int position) {     
  if(position < 1) {
    printf("\nposition should be >= 1.");
  } else if (position == 1 && *head_ref != NULL) {
    struct Node* nodeToDelete = *head_ref;
    *head_ref = (*head_ref)->next;
    free(nodeToDelete);
    if(*head_ref != NULL)
      (*head_ref)->prev = NULL;
  } else {
    struct Node *temp;
    temp = *head_ref;
    for(int i = 1; i < position-1; i++) {
      if(temp != NULL) {
        temp = temp->next;
      }
    }
    if(temp != NULL && temp->next != NULL) {
      struct Node* nodeToDelete = temp->next;
      temp->next = temp->next->next; 
      if(temp->next->next != NULL)
        temp->next->next->prev = temp->next;   
      free(nodeToDelete); 
    } else {
      printf("\nThe node is already null.");
    }       
  }
}    

//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);
  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 LinkedList
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

  #Delete an element at the given position
  def pop_at(self, position):     
    if(position < 1):
      print("\nposition should be >= 1.")
    elif (position == 1 and self.head != None):
      nodeToDelete = self.head
      self.head = self.head.next
      nodeToDelete = None
      if (self.head != None):
        self.head.prev = None
    else:    
      temp = self.head
      for i in range(1, position-1):
        if(temp != None):
          temp = temp.next   
      if(temp != None and temp.next != None):
        nodeToDelete = temp.next
        temp.next = temp.next.next
        if(temp.next.next != None):
          temp.next.next.prev = temp.next  
        nodeToDelete = None 
      else:
        print("\nThe node is already null.") 

  #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)
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.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;
    }    
  }

  //Delete an element at the given position
  void pop_at(int position) {     
    if(position < 1) {
      System.out.print("\nposition should be >= 1.");
    } else if (position == 1 && head != null) {
      Node nodeToDelete = head;
      head = head.next;
      nodeToDelete = null;
      if (head != null)
        head.prev = null;
    } else {
      Node temp = new Node();
      temp = head;
      for(int i = 1; i < position-1; i++) {
        if(temp != null) {
          temp = temp.next;
        }
      }
      if(temp != null && temp.next != null) {
        Node nodeToDelete = temp.next;
        temp.next = temp.next.next; 
        if(temp.next.next != null)
          temp.next.next.prev = temp.next;  
        nodeToDelete = null; 
      } else {
        System.out.print("\nThe node is already 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(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);
    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;
    } else {
      Node temp = new Node();
      temp = head;
      while(temp.next != null)
        temp = temp.next;
      temp.next = newNode;
      newNode.prev = temp;
    }    
  }

  //Delete an element at the given position
  public void pop_at(int position) {     
    if(position < 1) {
      Console.Write("\nposition should be >= 1.");
    } else if (position == 1 && head != null) {
      Node nodeToDelete = head;
      head = head.next;
      nodeToDelete = null;
      if (head != null)
        head.prev = null;
    } else {
      Node temp = new Node();
      temp = head;
      for(int i = 1; i < position-1; i++) {
        if(temp != null) {
          temp = temp.next;
        }
      }
      if(temp != null && temp.next != null) {
        Node nodeToDelete = temp.next;
        temp.next = temp.next.next; 
        if(temp.next.next != null)
          temp.next.next.prev = temp.next;   
        nodeToDelete = null;  
      } else {
        Console.Write("\nThe node is already 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(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);
    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;
    } else {
      $temp = new Node();
      $temp = $this->head;
      while($temp->next != null) {
        $temp = $temp->next;
      }
      $temp->next = $newNode;
      $newNode->prev = $temp;
    }    
  }

  //Delete an element at the given position
  public function pop_at($position) {     
    if($position < 1) {
      echo "\nposition should be >= 1.";
    } else if ($position == 1 && $this->head != null) {
      $nodeToDelete = $this->head;
      $this->head = $this->head->next;
      $nodeToDelete = null;
      if ($this->head != null)
        $this->head->prev = null;
    } else {
      $temp = new Node();
      $temp = $this->head;
      for($i = 1; $i < $position-1; $i++) {
        if($temp != null) {
          $temp = $temp->next;
        }
      }
      if($temp != null && $temp->next != null) {
        $nodeToDelete = $temp->next;
        $temp->next = $temp->next->next;
        if($temp->next->next != null)
          $temp->next->next->prev = $temp->next;   
        $nodeToDelete = null; 
      } else {
        echo "\nThe node is already null.";
      }       
    }
  } 

  //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);
$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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