From acdabf6f5a627e3d31cbd02d4536c61a2b45f328 Mon Sep 17 00:00:00 2001 From: Aditya Krishnakumar Date: Wed, 3 Oct 2018 23:56:43 +0530 Subject: [PATCH] linked_list.py: Add Linked List Data Structure in Python This commit adds the code for Linked List Data Structure in Python which has various common methods for inserting and deleting elements Closes https://github.com/NITSkmOS/Algorithms/issues/25 --- README.md | 2 +- linked_list/Python/linked_list.py | 176 ++++++++++++++++++++++++++++++ 2 files changed, 177 insertions(+), 1 deletion(-) create mode 100644 linked_list/Python/linked_list.py diff --git a/README.md b/README.md index 3ef986e2..bedd8b06 100644 --- a/README.md +++ b/README.md @@ -30,7 +30,7 @@ This repository contains examples of various algorithms written on different pro |:----------------------------------------------------------------------------------------------- |:-------------------------------------:|:-------------------------------------:|:-------------------------------------:|:-------------------------------------:| | [Queue](https://en.wikipedia.org/wiki/Queue_(abstract_data_type)) | | [:octocat:](queue/Cpp) | | | | [Stack](https://en.wikipedia.org/wiki/Stack_(abstract_data_type)) | | | [:octocat:](stack/Java) | [:octocat:](stack/Python) | -| [Linear Linked List](https://en.wikipedia.org/wiki/Linked_list) | [:octocat:](linked_list/C) | | | | +| [Linear Linked List](https://en.wikipedia.org/wiki/Linked_list) | [:octocat:](linked_list/C) | | | [:octocat:](linked_list/Python) | | [AVL Tree](https://en.wikipedia.org/wiki/AVL_tree) | [:octocat:](avl_tree/C) | | [:octocat:](avl_tree/Java) | [:octocat:](avl_tree/Python) | diff --git a/linked_list/Python/linked_list.py b/linked_list/Python/linked_list.py new file mode 100644 index 00000000..6df1207f --- /dev/null +++ b/linked_list/Python/linked_list.py @@ -0,0 +1,176 @@ +#!/usr/bin/env python3 + + +class NoSuchNodeException(Exception): + """Exception class""" + pass + + +class Node: + """ + Class for the structure of node in Linked List + + :param data: Data value for node + :param next_node: Next node reference + """ + + def __init__(self, data=None, next_node=None): + self.data = data + self.next_node = next_node + + def compare_to(self, node): + """ + Method to compare node data + + :return: Returns True if node data matches + """ + return node.data == self.data + + +class LinkedList: + """ + Class for the Linked List + :param head: Reference of the head. + :param list_size: List size. + """ + + def __init__(self, head=None, list_size=0): + self.head = head + self.list_size = list_size + + def size(self): + """ + This methods returns the size of the linked list. + + :return: The size of the linked list. + """ + return self.list_size + + def is_empty(self): + """ + This methods determines whether the list is empty. + :return: True if the list is empty, otherwise False. + """ + return self.list_size == 0 + + def get_first(self): + """ + This method returns the first element of the list. + + :return: The first element of the list. + """ + if self.is_empty(): + raise NoSuchNodeException() + + return self.head.data + + def getNode(self, i): + """ + This method takes an index and finds the node residing. + + :raises: NoSuchNodeException if no such element. + :param i: The index of the node. + :return: The ith node of the list. + """ + if i < 0 or i > self.list_size - 1: + raise NoSuchNodeException() + + current = 0 + p = self.head + + while current < i: + p = p.next_node + current += 1 + + return p + + def add_first(self, data): + """ + This method adds a node to the front of the list. + + :param data: The data of the node to add. + """ + node = Node(data, self.head) + self.head = node + + self.list_size += 1 + + def add_last(self, data): + """ + This method adds a node to the back of the list. + + :param data: The data of the node to add. + """ + node = Node(data, None) + + if self.is_empty(): + self.head = node + else: + tail = self.getNode(self.list_size - 1) + tail.next_node = node + + self.list_size += 1 + + def remove_first(self): + """ + This method removes the first element of the list. + + :return: The value of the first element. + """ + if self.is_empty(): + raise NoSuchNodeException() + + tmp_val = self.head.data + self.head = self.head.next_node + self.list_size -= 1 + return tmp_val + + def remove_last(self): + """ + This method removes the last element of the list. + + :return: The value of the removed element. + """ + if self.is_empty(): + raise NoSuchNodeException() + + tail = self.getNode(self.list_size - 1) + tail_data = tail.data + + if self.list_size == 1: + self.head = None + else: + before_tail = self.getNode(self.list_size - 2) + before_tail.next_node = None + + self.list_size -= 1 + return tail_data + + def print_list(self): + """ + Method to print the list in a newline after each element. + """ + p = self.head + i = 0 + + while i < self.size(): + print(p.data) + i += 1 + p = p.next_node + + +def main(): + myList = LinkedList() + myList.add_first(10) + myList.add_first(20) + myList.add_first(30) + print("Current List after adding 3 elements: ") + myList.print_list() + + myList.remove_last() + print("Current List after removing last element: ") + myList.print_list() + + +if __name__ == "__main__": + main()