Added Implementation of Singly Linked List in Python

python/Linked List/README.md

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+# Linked List
+A linked list is a sequence of data elements, which are connected together via links. Each data element contains a connection to another data element in form of a pointer. Python does not have linked lists in its standard library. We implement the concept of linked lists using the concept of nodes as discussed.
+There are three common types of Linked List.
+
+# Singly Linked List :-
+It is the most common. Each node has data and a pointer to the next node.
+
+# Doubly Linked List :-
+We add a pointer to the previous node in a doubly-linked list. Thus, we can go in either direction: forward or backward.
+
+# Circular Linked List :-
+A circular linked list is a variation of a linked list in which the last element is linked to the first element. This forms a circular loop.
+
+A circular linked list can be either singly linked or doubly linked.
+
+for singly linked list, next pointer of last item points to the first item
+In the doubly linked list, prev pointer of the first item points to the last item as well.

python/Linked List/Singly_LinkedList.py

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+class Node:
+    def __init__(self, item):
+        self.item = item 
+        self.next = None
+
+class LinkedList:
+    def __init__(self):
+        self.head = None
+
+    def to_linkedlist(self, input_list):
+        #Function to create a linked list from a input list.
+        self.tail = None
+
+        for item in input_list:
+            if self.head is None:
+                self.head = Node(item)
+                self.tail = self.head
+
+            else:
+                self.tail.next = Node(item)
+                self.tail = self.tail.next
+
+        return self.head
+
+    def append(self, item):
+        # function to add item to the end of linkedlist.
+
+        if self.head is None:
+            self.head = Node(item) # if linkedlist is empty 
+            return
+
+        # Now , moving to the end of linkedlist to add item if linkedlist is not empty.
+        node = self.head
+        while node.next:
+            node = node.next
+
+        node.next = Node(item)
+        return 
+
+    def prepend(self, item):
+        # function to add item at the front/beginning of the linkedlist.
+        if self.head is None:
+            self.head = Node(item) #when linkedlist is empty.
+            return
+
+        new_node = Node(item)
+        new_node.next = self.head
+        self.head = new_node # changing head of linkedlist to new node when linkedlist is not empty.
+
+    def pop(self):
+        # function returns the first node's item and remove it from the linkedlist.
+        if self.head is None:
+            return None
+
+        node = self.head
+        self.head = self.head.next
+
+        return node.item
+
+    def remove(self, item):
+        # delete the first coming node with the desired item .
+        if self.head is None:
+            return None  #when linkedlist is empty.
+
+        if self.head.item == item:
+            self.head = self.head.next
+            return
+
+        node = self.head
+        while node.next:
+            if node.next.item == item:
+                node.next = node.next.next
+                return 
+            node = node.next
+
+        print('Value not found')
+
+    def size(self):
+        #function returns the size of the linkedlist.
+        size = 0  # initialising size with value 0.
+        node = self.head
+        while node:
+            size += 1
+            node = node.next #Iterating through linkedlist.
+
+        return size
+
+
+
+    def to_list(self):
+        # Function to create a simple list from Linkedlist.
+        output_list = []
+
+        node = self.head
+
+        while node:
+            output_list.append(node.item)
+            node = node.next # loop terminates at last item of linkedlist.
+
+        return output_list
+