Implementing Data Structures & Algorithms using Python

Table of Contents

• Implementing Data Structures in Python
• Linked Lists
  • Implementation
  • Creating a LinkedList object
  • LinkedList Methods
  • Support for Built-in Python Functions
• Hash Tables
  • Creating a HashTable object
• Stacks
• Queues

---

Linked Lists

A linked list is a linear data structure that includes a series of connected nodes, where each node stores the data and the address of the next node.

Implementation

First, create a class that represents a Node of a linked list.

class Node:
    def __init__(self, data=None, next=None) -> None:
        self.data = data
        self.next = next

Then create another class that represents a LinkedList.

class LinkedList:
    def __init__(self) -> None:
        self.head = None
        self.n = 0
    ...

Creating a LinkedList object

To create an empty LinkedList object, do this:

>>> a = LinkedList()
>>> a
[ > ]

We can also create a LinkedList from an iterable object such as list, tuple, set, etc.
Example

>>> a = LinkedList.linkedlist(["h", "e", "l", "l", "o"])
>>> a
[ h > e > l > l > o ]

LinkedList Methods

The following methods can be used on LinkedList objects.

Method	Description
insert()	Adds an element at the specified position
pop()	Removes an element at the specified position
append()	Adds an element at the end of the LinkedList
remove()	Removes the first item with the specified value
clear()	Removes all the elements from a LinkedList
extend()	Appends all the elements of a sequence to the LinkedList

The LinkedList class also have a classmethod

• linkedlist() - Converts an iterable object into a LinkedList while preserving the order of items.

Usage:

>>> a = LinkedList.linkedlist([0, 1, 2, 3])
>>> a
[ 0 > 1 > 2 > 3 ]

Support for Built-in Python Functions

A LinkedList object supports the following built-in Python functions.

• print()
• str()
• len()
• iter()
• next()

Therefore, LinkedList objects are iterable which means you can iterate over them using a for loop.
e.g.

>>> for item in linkedlist:
>>>    print(item)

LinkedList objects also support indexing using square bracket notation (just like a list).
e.g.

>>> linkedlist[i] = "hello"
>>> print(linkedlist)
[ hello ]

You can also add two LinkedList objects together using the '+' operator.
e.g.

result = a + b  # where 'a' and 'b' are LinkedList objects

---

Hash Tables

The Hash table data structure stores elements in key-value pairs where

• key - unique integer that is used for indexing the values
• value - data that are associated with keys

Creating a HashTable object

You can create a HashTable object like this

table = HashTable()

Stacks

Queues