url.py

# Python3 code for above approach
def idToShortURL(id):
	map = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
	shortURL = ""
	
	# for each digit find the base 62
	while(id > 0):
		shortURL += map[id % 62]
		id //= 62

	# reversing the shortURL
	return shortURL[len(shortURL): : -1]

def shortURLToId(shortURL):
	id = 0
	for i in shortURL:
		val_i = ord(i)
		if(val_i >= ord('a') and val_i <= ord('z')):
			id = id*62 + val_i - ord('a')
		elif(val_i >= ord('A') and val_i <= ord('Z')):
			id = id*62 + val_i - ord('Z') + 26
		else:
			id = id*62 + val_i - ord('0') + 52
	return id

if (__name__ == "__main__"):
	id = 12345
	shortURL = idToShortURL(id)
	print("Short URL from 12345 is : ", shortURL)
	print("ID from", shortURL, "is : ", shortURLToId(shortURL))