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Python - Insert a new node at the start of the Linked List



In this method, a new node is inserted at the beginning of the linked list. For example - if the given List is 10->20->30 and a new element 100 is added at the start, the Linked List becomes 100->10->20->30.

Inserting a new node at the beginning of the Linked List is very easy. First, a new node with given element is created. It is then added before the head of the given Linked List that makes the newly added node to new head of the Linked List by changing the head pointer to point to the new node.

Linked List - Add Node At Start

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

def push_front(self, newElement):
  
  #1 & 2. allocate a new node
  #       and assign data element
  newNode = Node(newElement)
  
  #3. make next node of new node as head
  newNode.next = self.head
  
  #4. make new node as head 
  self.head = newNode 

The below is a complete program that uses above discussed concept to insert new node at the start of the linked list.

# node structure
class Node:
  def __init__(self, data):
    self.data = data
    self.next = None

#class Linked List
class LinkedList:
  def __init__(self):
    self.head = None

  #Add new element at the start of the list
  def push_front(self, newElement):
    newNode = Node(newElement)
    newNode.next = self.head 
    self.head = newNode   

  #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 start of the list.
MyList.push_front(10)
MyList.push_front(20)
MyList.push_front(30)
MyList.PrintList()

The above code will give the following output:

The list contains: 30 20 10 

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