171. Excel Sheet Column Number

def title_to_number(s):
    def alpha_to_num(letter):
        '''helper function'''
        # match = {'A': 1, 'B': 2, 'C': 3}   # Option 1: define a matching dictionary
        # return match[letter]
        return ord(letter) - ord('A') + 1    # Option 2: use ord()

    result = 0
    i = 0
    for char in reversed(s):
        result += alpha_to_num(char) * 26 ** i
        i += 1
    return result

from functools import reduce

def title_to_number(s):
    '''variations of above'''
    def alpha_to_num(letter):
        '''helper function'''
        return ord(letter) - ord('A') + 1

    result = 0

    # Option 1
    for char, i in zip(reversed(s), range(len(s))):
        result += alpha_to_num(char) * 26 ** i

    # Option 2
    for char in s:
        result = result*26 + alpha_to_num(char)

    # Option 3
    # using reduce(function, iterable, initializer)
    result = reduce(lambda result, x: result*26 + alpha_to_num(x), s, 0)
        
    return result