Linked List | Set 2 (Inserting a node)
We have introduced Linked Lists in the previous post. We also created a simple linked list with 3 nodes and discussed linked list traversal.
All programs discussed in this post consider the following representations of linked list.
C++
// A linked list node class Node { public: int data; Node *next; }; // This code is contributed by rathbhupendra |
C
// A linked list node struct Node { int data; struct Node *next; }; |
Java
// Linked List Class class LinkedList { Node head; // head of list /* Node Class */ class Node { int data; Node next;
// Constructor to create a new node Node(int d) {data = d; next = null; } } } |
Python
# Node class class Node: # Function to initialize the node object def __init__(self, data): self.data = data # Assign data self.next = None # Initialize next as null # Linked List class class LinkedList:
# Function to initialize the Linked List object def __init__(self): self.head = None |
C#
/* Linked list Node*/ public class Node { public int data; public Node next; public Node(int d) {data = d; next = null; } } |
Javascript
<script> // Linked List Class var head; // head of list /* Node Class */ class Node { // Constructor to create a new node constructor(d) { this.data = d; this.next = null; } } // This code is contributed by todaysgaurav </script> |
In this post, methods to insert a new node in linked list are discussed. A node can be added in three ways
1) At the front of the linked list
2) After a given node.
3) At the end of the linked list.
Python Program For Inserting A Node In A Linked List
We have introduced Linked Lists in the previous post. We also created a simple linked list with 3 nodes and discussed linked list traversal.
All programs discussed in this post consider the following representations of linked list.
Python
# Node class class Node:
# Function to initialize the # node object def __init__(self, data):
# Assign data self.data = data
# Initialize next as null self.next = None
# Linked List class class LinkedList:
# Function to initialize the # Linked List object def __init__(self): self.head = None |
In this post, methods to insert a new node in linked list are discussed. A node can be added in three ways
1) At the front of the linked list
2) After a given node.
3) At the end of the linked list.
Recommended: Please solve it on “PRACTICE” first, before moving on to the solution.
Add a node at the front: (4 steps process)
The new node is always added before the head of the given Linked List. And newly added node becomes the new head of the Linked List. For example, if the given Linked List is 10->15->20->25 and we add an item 5 at the front, then the Linked List becomes 5->10->15->20->25. Let us call the function that adds at the front of the list is push(). The push() must receive a pointer to the head pointer, because push must change the head pointer to point to the new node (See this)
Following are the 4 steps to add a node at the front.
Python
# This function is in LinkedList class # Function to insert a new node at # the beginning def push(self, new_data):
# 1 & 2: Allocate the Node & # Put in the data new_node = Node(new_data)
# 3. Make next of new Node as head new_node.next = self.head
# 4. Move the head to point to new Node self.head = new_node |
Time complexity of push() is O(1) as it does a constant amount of work.
Add a node after a given node: (5 steps process)
We are given a pointer to a node, and the new node is inserted after the given node.
Python
# This function is in LinkedList class. # Inserts a new node after the given # prev_node. This method is defined # inside LinkedList class shown above def insertAfter(self, prev_node, new_data):
# 1. Check if the given prev_node exists if prev_node is None: print "The given previous node must in LinkedList." return
# 2. Create new node & # 3. Put in the data new_node = Node(new_data)
# 4. Make next of new Node as next of prev_node new_node.next = prev_node.next
# 5. make next of prev_node as new_node prev_node.next = new_node |
Time complexity of insertAfter() is O(1) as it does a constant amount of work.
Add a node at the end: (6 steps process)
The new node is always added after the last node of the given Linked List. For example if the given Linked List is 5->10->15->20->25 and we add an item 30 at the end, then the Linked List becomes 5->10->15->20->25->30.
Since a Linked List is typically represented by the head of it, we have to traverse the list till the end and then change the next to last node to a new node.
Following are the 6 steps to add node at the end.
Python
# This function is defined in Linked List # class appends a new node at the end. # This method is defined inside LinkedList # class shown above def append(self, new_data): # 1. Create a new node # 2. Put in the data # 3. Set next as None new_node = Node(new_data) # 4. If the Linked List is empty, then # make the new node as head if self.head is None: self.head = new_node return # 5. Else traverse till the last node last = self.head while (last.next): last = last.next # 6. Change the next of last node last.next = new_node |
Time complexity of append is O(n) where n is the number of nodes in the linked list. Since there is a loop from head to end, the function does O(n) work.
This method can also be optimized to work in O(1) by keeping an extra pointer to the tail of the linked list/
Following is a complete program that uses all of the above methods to create a linked list.
Python
# A complete working Python program to demonstrate all # insertion methods of linked list
# Node class class Node:
# Function to initialize the # node object def __init__(self, data):
# Assign data self.data = data
# Initialize next as null self.next = None
# Linked List class contains a # Node object class LinkedList:
# Function to initialize head def __init__(self): self.head = None
# Functio to insert a new node at # the beginning def push(self, new_data):
# 1 & 2: Allocate the Node & # Put in the data new_node = Node(new_data)
# 3. Make next of new Node as head new_node.next = self.head
# 4. Move the head to point to new Node self.head = new_node
# This function is in LinkedList class. # Inserts a new node after the given # prev_node. This method is defined # inside LinkedList class shown above def insertAfter(self, prev_node, new_data):
# 1. Check if the given prev_node exists if prev_node is None: print "The given previous node must inLinkedList." return
# 2. Create new node & # Put in the data new_node = Node(new_data)
# 4. Make next of new Node as next # of prev_node new_node.next = prev_node.next
# 5. make next of prev_node as new_node prev_node.next = new_node
# This function is defined in Linked List class # Appends a new node at the end. This method is # defined inside LinkedList class shown above */ def append(self, new_data):
# 1. Create a new node # 2. Put in the data # 3. Set next as None new_node = Node(new_data)
# 4. If the Linked List is empty, then make the # new node as head if self.head is None: self.head = new_node return
# 5. Else traverse till the last node last = self.head while (last.next): last = last.next
# 6. Change the next of last node last.next = new_node
# Utility function to print the # linked list def printList(self): temp = self.head while (temp): print temp.data, temp = temp.next
# Code execution starts here if __name__=='__main__':
# Start with the empty list llist = LinkedList()
# Insert 6. So linked list becomes 6->None llist.append(6)
# Insert 7 at the beginning. So # linked list becomes 7->6->None llist.push(7);
# Insert 1 at the beginning. So # linked list becomes 1->7->6->None llist.push(1);
# Insert 4 at the end. So linked list # becomes 1->7->6->4->None llist.append(4)
# Insert 8, after 7. So linked list # becomes 1 -> 7-> 8-> 6-> 4-> None llist.insertAfter(llist.head.next, 8)
print 'Created linked list is:', llist.printList() # This code is contributed by Manikantan Narasimhan |
Output:
Created Linked list is: 1 7 8 6 4Please refer complete article on Linked List | Set 2 (Inserting a node) for more details!
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A linked list is a sequence of data elements, which are connected together via links. Each data element contains a connection to another data element in form of a pointer. Python does not have linked lists in its standard library. We implement the concept of linked lists using the concept of nodes as discussed in the previous chapter.
We have already seen how we create a node class and how to traverse the elements of a node.In this chapter we are going to study the types of linked lists known as singly linked lists. In this type of data structure there is only one link between any two data elements. We create such a list and create additional methods to insert, update and remove elements from the list.
Linked Lists in Python: An Introduction
by Pedro Pregueiro intermediate python Mark as Completed Tweet Share Email
Table of Contents
Remove adsWatch Now This tutorial has a related video course created by the Real Python team. Watch it together with the written tutorial to deepen your understanding: Working With Linked Lists in Python
Linked lists are like a lesser-known cousin of lists. They’re not as popular or as cool, and you might not even remember them from your algorithms class. But in the right context, they can really shine.
In this article, you’ll learn:
- What linked lists are and when you should use them
- How to use collections.deque for all of your linked list needs
- How to implement your own linked lists
- What the other types of linked lists are and what they can be used for
If you’re looking to brush up on your coding skills for a job interview, or if you want to learn more about Python data structures besides the usual dictionaries and lists, then you’ve come to the right place!
You can follow along with the examples in this tutorial by downloading the source code available at the link below:
Get the Source Code: Click here to get the source code you’ll use to learn about linked lists in this tutorial.
Linked List Operations: Traverse, Insert and Delete
In this tutorial, you will learn different operations on a linked list. Also, you will find implementation of linked list operations in C/C++, Python and Java.
There are various linked list operations that allow us to perform different actions on linked lists. For example, the insertion operation adds a new element to the linked list.
Here's a list of basic linked list operations that we will cover in this article.
- Traversal - access each element of the linked list
- Insertion - adds a new element to the linked list
- Deletion - removes the existing elements
- Search - find a node in the linked list
- Sort - sort the nodes of the linked list
Before you learn about linked list operations in detail, make sure to know about Linked List first.
Things to Remember about Linked List
- head points to the first node of the linked list
- next pointer of the last node is NULL, so if the next current node is NULL, we have reached the end of the linked list.
In all of the examples, we will assume that the linked list has three nodes 1 --->2 --->3 with node structure as below:
struct node { int data; struct node *next; };