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Python Program for Deleting a Node in a Linked List

  • Last Updated : 18 May, 2022

We have discussed Linked List Introduction and Linked List Insertion in previous posts on a singly linked list.
Let us formulate the problem statement to understand the deletion process. Given a ‘key’, delete the first occurrence of this key in the linked list

Iterative Method:
To delete a node from the linked list, we need to do the following steps. 
1) Find the previous node of the node to be deleted. 
2) Change the next of the previous node. 
3) Free memory for the node to be deleted.
 

linkedlist_deletion

 

Since every node of the linked list is dynamically allocated using malloc() in C, we need to call free() for freeing memory allocated for the node to be deleted.

Python3




# A complete working Python3 program to
# demonstrate deletion in singly 
# linked list with class 
  
# Node class 
class Node: 
  
    # Constructor to initialize the node object 
    def __init__(self, data): 
        self.data = data 
        self.next = None
  
class LinkedList: 
  
    # Function to initialize head 
    def __init__(self): 
        self.head = None
  
    # Function to insert a new node at the beginning 
    def push(self, new_data): 
        new_node = Node(new_data) 
        new_node.next = self.head 
        self.head = new_node 
  
    # Given a reference to the head of a list and a key, 
    # delete the first occurrence of key in linked list 
    def deleteNode(self, key): 
          
        # Store head node 
        temp = self.head 
  
        # If head node itself holds the key to be deleted 
        if (temp is not None): 
            if (temp.data == key): 
                self.head = temp.next
                temp = None
                return
  
        # Search for the key to be deleted, keep track of the 
        # previous node as we need to change 'prev.next' 
        while(temp is not None): 
            if temp.data == key: 
                break
            prev = temp 
            temp = temp.next
  
        # if key was not present in linked list 
        if(temp == None): 
            return
  
        # Unlink the node from linked list 
        prev.next = temp.next
  
        temp = None
  
  
    # Utility function to print the linked LinkedList 
    def printList(self): 
        temp = self.head 
        while(temp): 
            print (" %d" %(temp.data)), 
            temp = temp.next
  
  
# Driver program 
llist = LinkedList() 
llist.push(7
llist.push(1
llist.push(3
llist.push(2
  
print ("Created Linked List: ")
llist.printList() 
llist.deleteNode(1
print ("
Linked List after Deletion of 1:")
llist.printList() 
  
# This code is contributed by Nikhil Kumar Singh (nickzuck_007) 


Output:
Created Linked List: 
 2  3  1  7 
Linked List after Deletion of 1: 
 2  3  7

Please refer complete article on Linked List | Set 3 (Deleting a node) for more details!


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