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Python Program for Deleting a Node in a Linked List

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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) & edited by Sayan Biswas (dankguy6146)


Output

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

Time Complexity: O(n), where n represents the length of the given linked list.
Auxiliary Space: O(1), no extra space is required, so it is a constant.

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



Last Updated : 24 Apr, 2023
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