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× Python Data Structures - Doubly Linked List Other Related Topics


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.

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
      nodeToDelete = None 
    else:
      
      #5. Else the given node will be empty.
      print("\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.

# 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
        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("\nThe list contains:", end=" ")
      while (temp != None):
        print(temp.data, end=" ")
        temp = temp.next
    else:
      print("\nThe 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()

#Insert 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