# Python program to reverse a linked list
# Time Complexity : O(n)
# Space Complexity : O(n) as 'next'
#variable is getting created in each loop.

# Node class


class Node:

	# Constructor to initialize the node object
	def __init__(self, data):
		self.data = data
		self.next = None


class LinkedList:

	# Function to initialize head
	def __init__(self):
		self.head = None

	# Function to reverse the linked list
	def reverse(self):
		prev = None
		current = self.head
		while(current is not None):
			next = current.next
			current.next = prev
			prev = current
			current = next
		self.head = prev

	# Function to insert a new node at the beginning
	def push(self, new_data):
		new_node = Node(new_data)
		new_node.next = self.head
		self.head = new_node

	# Utility function to print the linked LinkedList
	def printList(self):
		temp = self.head
		while(temp):
			print temp.data,
			temp = temp.next


# Driver program to test above functions
llist = LinkedList()
llist.push(20)
llist.push(4)
llist.push(15)
llist.push(85)

print "Given Linked List"
llist.printList()
llist.reverse()
print "\nReversed Linked List"
llist.printList()

import os

# Get the current directory
current_dir = os.getcwd()

# Loop through each file in the current directory
for filename in os.listdir(current_dir):

    # Check if the file name starts with a number followed by a period and a space
    if filename[0].isdigit() and filename[1] == '.' and filename[2] == ' ':
        
        # Remove the number, period, and space from the file name
        new_filename = filename[3:]
        
        # Rename the file
        os.rename(os.path.join(current_dir, filename), os.path.join(current_dir, new_filename))

from datetime import datetime

epoch_time = 1753823646  # Example epoch time (March 15, 2023 00:00:00 UTC)

# Convert epoch time to a UTC datetime object
utc_datetime = datetime.utcfromtimestamp(epoch_time)

print(f"Epoch time: {epoch_time}")
print(f"UTC datetime: {utc_datetime}")

# You can also format the output string
formatted_utc_time = utc_datetime.strftime('%m-%d-%Y %H:%M:%S UTC')
print(f"Formatted UTC datetime: {formatted_utc_time}")

import math

def factorial(n):
    print(math.factorial(n))
    return (math.factorial(n))
    
factorial(5)
factorial(10)
factorial(15)

import itertools

def compute_permutations(string):
    # Generate all permutations of the string
    permutations = itertools.permutations(string)

    # Convert each permutation tuple to a string
    permutations = [''.join(permutation) for permutation in permutations]

    return permutations

# Prompt the user for a string
string = input("Enter a string: ")

# Compute permutations
permutations = compute_permutations(string)

# Display the permutations
print("Permutations:")
for permutation in permutations:
    print(permutation)

filename = "data.txt"
data = "Hello, World!"

with open(filename, "a") as file:
    file.write(data)