Linked Lists

Linked List Data Structure

A linked list is a data structure that consists of a list of nodes. Each node contains data and a link to the next node. As shown below, you can implement a LinkedList class in Python, utilizing a Python implementation of the Node class.

class LinkedList:
  def __init__(self, value=None):
    self.head_node = Node(value)

  def get_head_node(self):
    return self.head_node

  def insert_beginning(self, new_value):
    new_node = Node(new_value)
    new_node.set_next_node(self.head_node)
    self.head_node = new_node

  def stringify_list(self):
    string_list = ""
    current_node = self.get_head_node()
    while current_node:
      if current_node.get_value() != None:
        string_list += str(current_node.get_value()) + "\n"
      current_node = current_node.get_next_node()
    return string_list

  def remove_node(self, value_to_remove):
    current_node = self.get_head_node()
    if current_node.get_value() == value_to_remove:
      self.head_node = current_node.get_next_node()
    else:
      while current_node:
        next_node = current_node.get_next_node()
        if next_node.get_value() == value_to_remove:
          current_node.set_next_node(next_node.get_next_node())
          current_node = None
        else:
          current_node = next_node

Removing a node from the middle of a linked list

When removing a node from the middle of a linked list, it is necessary to adjust the link on the previous node so that it points to the following node. In the given illustration, the node a1 must point to the node a3 if the node a2 is removed from the linked list.

Linked List data structure

A linked list is a linear data structure where elements are not stored at contiguous location. Instead the elements are linked using pointers.

In a linked list data is stored in nodes and each node is linked to the next and, optionally, to the previous. Each node in a list consists of the following parts:

data
A pointer (Or reference) to the next node
Optionally, a pointer to the previous node

A linked list with each node holding its data and pointing to the next node.

Adding a new head node in a linked list

When adding a new node to the start of a linked list, it is necessary to maintain the list by giving the new head node a link to the current head node. For instance, to add a new node a0 to the begining of the linked list, a0 should point to a1.

The Head Node in Linked Lists

The first node in a linked list is called the head node. If the linked list is empty, then the value of the head node is NULL.

A linked list structure with Head and Tail pointers.

Implementing a linked list

A linked list exposes the ability to traverse the list from one node to another node. The starting node is considered the head node from where the list can be traversed.