Hi there! 
You have to implement the 

`String get_column_title(int num) // syntax depends on programming language`

function that takes an integer number (index of the Excel column) and returns the string represents the title of this column.

#Intro
In the MS Excel lines are numbered by decimals, columns - by sets of letters.

For example, the first column has the title "A", second column - "B", 26th - "Z", 27th - "AA". 

"BA"(53) comes after "AZ"(52), "AAA" comes after "ZZ".




Excel? Columns? More details [here](https://en.wikipedia.org/wiki/Microsoft_Excel)

#Input
It takes only one argument - column decimal index number.
Argument `num` is a natural number.

#Output
Output is the upper-case string represents the title of column. It contains the English letters: A..Z

#Errors
For cases `num < 1` your function should throw/raise `IndexError`. In case of non-integer argument you should throw/raise `TypeError`.

In Java, you should throw `Exceptions`.

Nothing should be returned in Haskell.

#Examples
Python, Ruby:
```
>>> get_column_title(52)
"AZ"
>>> get_column_title(1337)
"AYK"
>>> get_column_title(432778)
"XPEH"
>>> get_column_title()
TypeError:
>>> get_column_title("123")
TypeError:
>>> get_column_title(0)
IndexError:
```
JS, Java:
```
>>> getColumnTitle(52)
"AZ"
>>> getColumnTitle(1337)
"AYK"
>>> getColumnTitle(432778)
"XPEH"
>>> getColumnTitle()
TypeError:
>>> getColumnTitle("123")
TypeError:
>>> getColumnTitle(0)
IndexError:
```

#Hint
The difference between the 26-digits notation and Excel columns numeration that in the first system, after "Z" there are "BA", "BB", ..., while in the Excel columns scale there is a range of 26 elements: AA, AB, ... , AZ between Z and BA. 

It is as if in the decimal notation was the following order: 0, 1, 2, .., 9, 00, 01, 02, .., 09, 10, 11, .., 19, 20..29..99, 000, 001 and so on.

#Also
The task is really sapid and hard. If you're stuck - write to the discussion board, there are many smart people willing to help.

Difficulty: EASY
Starter code: def get_column_title(num):
	

Solutions:
from string import ascii_uppercase as u

def get_column_title(n):
	assert isinstance(n, int) and n > 0
	col = []
	while n:
		(n, r) = divmod(n - 1, 26)
		col.append(u[r])
	return ''.join(reversed(col))


upper = __import__('string').ascii_uppercase.__getitem__

def get_column_title(num=None):
	if not isinstance(num, int):
		raise TypeError()
	if num < 1:
		raise IndexError()
	res = []
	while num:
		(num, r) = divmod(num - 1, 26)
		res.append(r)
	return ''.join(map(upper, reversed(res)))


alpha = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'

def get_column_title(n):
	if n < 1:
		raise ValueError
	l = []
	while n:
		(n, m) = divmod(n - 1, 26)
		l.append(alpha[m])
	return ''.join(l[::-1])


from string import ascii_uppercase

def get_column_title(n):
	n -= 1
	result = []
	while n >= 0:
		result.append(ascii_uppercase[n % 26])
		n = n // 26 - 1
	if not result:
		raise ValueError('Not a valid number.')
	return ''.join(result[::-1])


def get_column_title(num):
	if type(num) != int:
		raise TypeError
	if num < 1:
		raise IndexError
	abc = ' ABCDEFGHIJKLMNOPQRSTUVWXYZ'
	col_title = ''
	while num > 0:
		letter_index = num % 26
		if letter_index == 0:
			letter_index = 26
			num -= 26
		num //= 26
		col_title = abc[letter_index] + col_title
	return col_title.strip()


def get_column_title(number):
	if number <= 0:
		raise ValueError
	if number <= 26:
		return chr(number + 64)
	else:
		return get_column_title((number - 1) // 26) + chr(65 + (number - 1) % 26)


alphabet = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'

def get_column_title(number):
	result = []
	if not isinstance(number, int):
		raise TypeError

	def convert(num):
		if isinstance(num, list):
			n = num[0]
		else:
			if len(result) == 0:
				result.append(num)
			n = num
		if 0 < n <= 26:
			result.append(alphabet[n - 1])
			return result
		else:
			if n % 26 == 0:
				result[0] = convert(n // 26 - 1)
			else:
				result[0] = convert(n // 26)
			result.append(alphabet[n % 26 - 1])
			return result
	res = convert(number)
	result = []
	return ''.join(res[1:])


def get_column_title(num):
	if num <= 0:
		raise 'IndexError'
	elif type(num) != int:
		raise 'TypeError'
	else:
		string = ''
		while num > 0:
			(num, remainder) = divmod(num - 1, 26)
			string = chr(65 + remainder) + string
		return string


def get_column_title(num):
	if num < 1:
		return error
	a = [num % 26]
	while num > 26:
		num = num // 26 - 1
		a += [num % 26 + 1]
	y = a + [num] if num > 26 else a
	if y[0] == 0 and len(y) > 1:
		y[1] -= 1
	return ''.join(['Z' if i == 0 else chr(i + ord('A') - 1) for i in y][::-1])


from itertools import count

def get_column_title(num):
	if num < 1:
		raise IndexError
	if num <= 26:
		return chr(ord('A') + num - 1)
	return get_column_title((num - 1) // 26) + get_column_title(1 + (num - 1) % 26)