Broken digits

Weekly Challenge 275

Each week Mohammad S. Anwar sends out The Weekly Challenge, a chance for all of us to come up with solutions to two weekly tasks. My solutions are written in Python first, and then converted to Perl. It's a great way for us all to practice some coding.

Challenge, My solutions

Task 1: Broken Keys

Task

You are given a sentence, $sentence and list of broken keys @keys.

Write a script to find out how many words can be typed fully.

My solution

Two relativity straight forward tasks this week. For this task, I split the str variable into the words list (array in Perl), converting the string to lower case. I also convert the keys list to lower case too. I have a variable count that is original set to zero. This is the number of words that don't contain a broken key.

def broken_keys(s: str, keys: list) -> int:
    words = s.lower().split(' ')
    keys = [key.lower() for key in keys]
    count = 0

I then loop through each words value as the variable word. If none (not any) of the letters in keys is in word, I add one to the count variable.

    for word in words:
        if not any(key in word for key in keys):
            count += 1

    return count

Examples

$ ./ch-1.py "Perl Weekly Challenge" l a
0

$ ./ch-1.py "Perl and Raku" a
1

$ ./ch-1.py "Well done Team PWC" l o
2

$ ./ch-1.py "The joys of polyglottism" T
2

Task 2: Replace Digits

Task

You are given an alphanumeric string, $str, where each character is either a letter or a digit.

Write a script to replace each digit in the given string with the value of the previous letter plus (digit) places.

My solution

There are two unanswered questions that the examples don't shed a light on.

1. What happens when a number appears before the first letter? I treat this as an error, and exit the program with an appropriate message.
2. What is the output of z1? If this occurs, I roll over the alphabet. For example z1 is a, y3 is b.

I start with the following variables:

• current_letter which is the last seen letter (default is None)
• solution which represents the solution. It starts as an empty string.
• alphabet is a string of the 26 letters of the alphabet.

I loop through each letter of the str value, as the variable char. If it is a number, I calculate the index of the last letter, add char (as an integer) to it, and add the corresponding letter of the alphabet to the solution string. If it is a letter, I add it to the solution string and update current_letter.

def replace_digits(s: str) -> str:
    current_letter = None
    solution = ''
    alphabet = string.ascii_lowercase

    for char in s:
        if char.isdigit():
            if current_letter is None:
                raise ValueError('The first number must follow a letter.')
            solution += alphabet[(alphabet.index(current_letter) +
                                  int(char)) % 26]
        else:
            solution += char
            current_letter = char

    return solution

Examples

$ ./ch-2.py a1c1e1
abcdef

$ ./ch-2.py a1b2c3d4
abbdcfdh

$ ./ch-2.py b2b
bdb

$ ./ch-2.py a16z
abgz