class Node: # create a Node def __init__(self, data): self.data = data # given data self.next = None # given next to None def __repr__(self): # string representation of a Node return f"Node({self.data})" class LinkedList: def __init__(self): self.head = None # initialize head to None def insert_tail(self, data) -> None: if self.head is None: self.insert_head(data) # if this is first node, call insert_head else: temp = self.head while temp.next: # traverse to last node temp = temp.next temp.next = Node(data) # create node & link to tail def insert_head(self, data) -> None: newNod = Node(data) # create a new node if self.head: newNod.next = self.head # link newNode to head self.head = newNod # make NewNode as head def print_list(self) -> None: # print every node data temp = self.head while temp: print(temp.data) temp = temp.next def delete_head(self): # delete from head temp = self.head if self.head: self.head = self.head.next temp.next = None return temp def delete_tail(self): # delete from tail temp = self.head if self.head: if self.head.next is None: # if head is the only Node in the Linked List self.head = None else: while temp.next.next: # find the 2nd last element temp = temp.next # (2nd last element).next = None and temp = last element temp.next, temp = None, temp.next return temp def is_empty(self) -> bool: return self.head is None # return True if head is none def reverse(self): prev = None current = self.head while current: # Store the current node's next node. next_node = current.next # Make the current node's next point backwards current.next = prev # Make the previous node be the current node prev = current # Make the current node the next node (to progress iteration) current = next_node # Return prev in order to put the head at the end self.head = prev def __repr__(self): # String representation/visualization of a Linked Lists current = self.head string_repr = "" while current: string_repr += f"{current} --> " current = current.next # END represents end of the LinkedList return string_repr + "END" # Indexing Support. Used to get a node at particaular position def __getitem__(self, index): current = self.head # If LinkedList is empty if current is None: raise IndexError("The Linked List is empty") # Move Forward 'index' times for _ in range(index): # If the LinkedList ends before reaching specified node if current.next is None: raise IndexError("Index out of range.") current = current.next return current # Used to change the data of a particular node def __setitem__(self, index, data): current = self.head # If list is empty if current is None: raise IndexError("The Linked List is empty") for i in range(index): if current.next is None: raise IndexError("Index out of range.") current = current.next current.data = data def main(): A = LinkedList() A.insert_head(input("Inserting 1st at head ").strip()) A.insert_head(input("Inserting 2nd at head ").strip()) print("\nPrint list:") A.print_list() A.insert_tail(input("\nInserting 1st at tail ").strip()) A.insert_tail(input("Inserting 2nd at tail ").strip()) print("\nPrint list:") A.print_list() print("\nDelete head") A.delete_head() print("Delete tail") A.delete_tail() print("\nPrint list:") A.print_list() print("\nReverse linked list") A.reverse() print("\nPrint list:") A.print_list() print("\nString representation of linked list:") print(A) print("\nReading/changing Node data using indexing:") print(f"Element at Position 1: {A[1]}") A[1] = input("Enter New Value: ").strip() print("New list:") print(A) if __name__ == "__main__": main()