Peter Campbell Smith

Common characters and
squareful sequences

Weekly challenge 220 — 5 June 2023

Week 220 - 5 Jun 2023

Task 1

Task — Common characters

You are given a list of words. Write a script to return the list of characters (sorted alphabetically) found in every word of the given list.


The simplest way to do this, I think is to start with $word[0] and then delete from it every character not found in each other word, like this: for $w (1 .. scalar @words - 1) {
    $words[0] =~ s|[^$words[$w]]||gi;

$words[0] now contains only letters which also occur in every other word and it only remains to split them into an array and sort the array.

Try it 

Example: pot, spot, trot



use v5.16;    # The Weekly Challenge - 2023-06-05
use utf8;     # Week 220 task 1 - Common characters
use strict;   # Peter Campbell Smith
use warnings; # Blog:

common_characters('Perl', 'Rust', 'Raku');
common_characters('mouse', 'house', 'esoteric', 'some', 'mesolithic', 'Thames', 'semibreve'); 
common_characters('ring', 'sing', 'ping', 'zing', 'shopping', 'single', 'mingle', 'gin');

sub common_characters {
    my (@words, $w, @letters);
    # delete from $word[0] any letters not in all the other words
    @words = @_;
    for $w (1 .. scalar @words - 1) {
        $words[0] =~ s|[^$words[$w]]||gi;

    @letters = sort(split('', lc($words[0])));

    # show results
    say qq[\nInput:  \@words = ('] . join(qq[', '], @_) . q[')];
    say qq[Output: ('] . join(qq[', '], @letters) . q[')];


Input:  @words = ('Perl', 'Rust', 'Raku')
Output: ('r')

Input:  @words = ('mouse', 'house', 'esoteric', 'some', 'mesolithic', 'Thames', 'semibreve')
Output: ('e', 's')

Input:  @words = ('ring', 'sing', 'ping', 'zing', 'shopping', 'single', 'mingle', 'gin')
Output: ('g', 'i', 'n')

The content of this website which has been created by
Peter Campbell Smith is hereby placed in the public domain