Linked List | Set 1 (Introduction)
Like arrays, Linked List is a linear data structure. Unlike arrays,
linked list elements are not stored at contiguous location; the elements are linked using pointers.

linkedlist

Why Linked List?
Arrays can be used to store linear data of similar types, but arrays have following limitations.
1) The size of the arrays is fixed: So we must know the upper limit on the number of elements in advance.
Also, generally, the allocated memory is equal to the upper limit irrespective of the usage.
2) Inserting a new element in an array of elements is expensive, because room has to be created for the
 new elements and to create room existing elements have to shifted.

For example, in a system if we maintain a sorted list of IDs in an array id[].

id[] = [1000, 1010, 1050, 2000, 2040].
And if we want to insert a new ID 1005, then to maintain the sorted order, we have to move all the elements
after 1000 (excluding 1000).
Deletion is also expensive with arrays until unless some special techniques are used.
For example, to delete 1010 in id[], everything after 1010 has to be moved.

Advantages over arrays
1) Dynamic size
2) Ease of insertion/deletion

Drawbacks:
1) Random access is not allowed. We have to access elements sequentially starting from the first node.
 So we cannot do binary search with linked lists.
2) Extra memory space for a pointer is required with each element of the list.
3) Not cache friendly. Since array elements are contiguous locations, there is locality of reference
 which is not there in case of linked lists.

Representationv:
A linked list is represented by a pointer to the first node of the linked list.
 The first node is called head. If the linked list is empty, then value of head is NULL.
Each node in a list consists of at least two parts:
1) data
2) Pointer (Or Reference) to the next node
In Java, LinkedList can be represented as a class and a Node as a separate class.
The LinkedList class contains a reference of Node class type.

# 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

class LinkedList
{
    Node head;  // head of list

    /* Linked list Node*/
    class Node
    {
        int data;
        Node next;

        // Constructor to create a new node
        // Next is by default initialized
        // as null
        Node(int d) {data = d;}
    }
}