missing_letters.py

"""
This week’s question:
Write a function that takes an array of consecutive, increasing letters as input, and returns any missing letters in the array between the first and last letter.

Example:
> missingLetters(['a','b','c','d','f'])
> ['e']
> missingLetters(['a','b','c','d','e','h','i','j','k','l','m','n','o','p','q','r','s','t','u','w','x','y','z'])
> ['f','g','v']
"""

from typing import List

def missing_letters(letters: List[str]):
    """Given a list of letters in alphabetical order, return a list of missing letters.
    >>> missing_letters(['a','b','c','d','f'])
    ['e']
    >>> missing_letters(['a','b','c','d','e','h','i','j','k','l','m','n','o','p','q','r','s','t','u','w','x','y','z'])
    ['f', 'g', 'v']
    """

    # The `ord` function returns the ASCII representation given a character.
    # The `chr` function does the inverse (returns character given ASCII number).
    return [
        chr(c)
        for c in range(ord(letters[0]), ord(letters[-1]))
        if chr(c) not in letters
    ]


if __name__ == "__main__":
    import doctest
    doctest.testmod()