Matching and zipping

Weekly Challenge 256

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: Maximum Pairs

Task

You are given an array of distinct words, @words.

Write a script to find the maximum pairs in the given array. The words $words[i] and $words[j] can be a pair one is reverse of the other

My solution

For this task, I have a loop that takes the last value from the words array and store it in the word variable. I then see if its reverse is in the words array, and increment the count if it is. I continue this until the original array is exhausted.

def count_pairs(words: list) -> int:
    count = 0

    while words:
        word = words.pop()

        if word[::-1] in words:
            count += 1

    return count

Examples

$ ./ch-1.py ab de ed bc
1

$ ./ch-1.py aa ba cd ed
0

$ ./ch-1.py uv qp st vu mn pq
2

Task 2: Merge Strings

Task

You are given two strings, $str1 and $str2.

Write a script to merge the given strings by adding in alternative order starting with the first string. If a string is longer than the other then append the remaining at the end.

My solution

My solution will take any number of strings, be it one, two (as per the task) or more. Thankfully Python has the zip_longest function from itertools to make the task a one-liner.

def merge_strings(words: list) -> str:
    return ''.join(''.join(s) for s in zip_longest(*words, fillvalue=''))

The zip_longest function returns a iterable of tuples (with an empty string if one list is exhausted). The inner join turns this into a list of strings. The outer join turns this into a string.

The Perl solution follows a similar logic, and uses the mesh function from List::Util. The first lines converts an array of strings into an array of single characters. The mesh function returns a flat array, so only a single join statement is required.

sub main (@words) {
    my @arrays = map { [ split // ] } @words;
    say join( '', mesh(@arrays) );
}

Examples

$ ./ch-2.py abcd 1234
a1b2c3d4

$ ./ch-2.py abc 12345
a1b2c345

$ ./ch-2.py abcde 123
a1b2c3de