Thursday, 3 October 2019

Implementing generic Linked List with O(n) time complexity for Addition


Implementing generic linked list and performing basic operation on them with O(1) time complexity is easier than what the developers think. It's just the hype of Data Structures and the word Time Complexity.


Linked list is basically a object which holds of another object of same type and so on for every other object until the reference to next object becomes null. What is this reference? It’s just a reference variable which has an object.


To understand this better let’s take an example.
How many of you have seen Naruto? Well specific for this answer I’m going to get little less views :-D

Do you understand the word Izanmi
In this every instance which Kabuto experience is an object which hold a reference to another instance and so on until null is reached
Getting it.

Now lets move to coding example-

using System;
using System.Collections.Generic;

namespace Stucts.ADT.GenericLinkedList
{
    public class Node<T>
    {
        public T data;
        public Node<T> next = null;
    }
}

It’s a simple class which have one variable to hold data and one to hold the reference of same type of object

using System;
using System.Collections.Generic;

namespace Stucts.ADT.GenericLinkedList
{
    public class SimpleGenericLinkedList<T>
    {
        Node<T> head = null;
        Node<T> tail = null;

        private Node<T> CreateNode(T data, Node<T> next)
        {
            Node<T> newItem = new Node<T>();
            newItem.data = data;
            newItem.next = next;
            return newItem;
        }


        public void Add(T data)
        {
            if (head == null)
            {
                head = CreateNode(data, null);
                tail = head;
            }
            else {
                tail.next = CreateNode(data,null);
                tail = tail.next;
            }
        }

        public void RemoveNode(T data)
        {
            if (head.data.Equals(data))
            {
                head = head.next;
            }
            else
            {
                head.next = Remove(data, head.next);
            }
        }

        public Node<T> Remove(T data, Node<T> current)
        {
            if (current != null)
            {
                if (current.data.Equals(data))
                {
                    current = current.next;
                }
                else
                {
                    current.next = Remove(data, current.next);
                }
            }
            return current;
        }

        public void ReadAll()
        {
            Node<T> current = head;
            while (current.next != null)
            {
                Console.WriteLine(current.data); ;
                current = current.next;
            }
            Console.WriteLine(current.data); ;
        }
    }
}

Here I have performed some vary basic operation like adding, removing from head and traversing the entire list
Now to insert every new node in linked list we need to traverse through all the nodes and then add the node in the last.
Due to this traversal adding new node in linked list becomes time consuming and less effective with Time Complexity of O(n). This is clearly an issue. We can solve this by performing one very basic step while adding every node
In your Generic Linked list class add Tail node just like Head and when you add new node make it tail and keep adding new elements to tail.

SimpleGenericLinkedList<int> lnkList = new SimpleGenericLinkedList<int>();
            lnkList.Add(1);
            lnkList.Add(2);
            lnkList.Add(3);
            lnkList.Add(4);
            lnkList.Add(5);
            lnkList.Add(6);
            lnkList.Add(7);
            lnkList.Add(8);
            lnkList.Add(9);
            lnkList.Add(10);
            lnkList.RemoveNode(6);
            lnkList.ReadAll();


This is how the linked list object looks like


Just look at the object lnkList for every new node it has next and that next has another next and goes on until the lnkList.next.next….next == null;



Well that’s how linked list works and with just an easy step you can perform addition in linked list cost effective i.e. O(1)

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Thanks.

1 comment:

  1. how can implements a cantainsKey() method in the custom Dictionary class

    ReplyDelete

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