TWC328

 Challenge Link

Task1

We replace the ? mark with the first letter that isn't in the string already:

#!/usr/bin/env perl
use strict;
use warnings;

sub replace_all{
  my %h = map{$_ => 1} split '',$_[0];
  my @chars = grep{!exists $h{$_}} 'a'..'z';
  $_[0] =~ s/\?/$chars[0]/r
}

printf "%s\n",replace_all('a?z');
printf "%s\n",replace_all('pe?k');
printf "%s\n",replace_all('gra?te');

Task2

As long as there are pairs of consecutive capital and lowercase letters (irrespective of their order), we remove it from the string:

#!/usr/bin/env perl
use strict;
use warnings;

sub good_string{
  my ($str) = @_;
  my $chars = join '|',map{"$_\u$_|\u$_$_"} 'a'..'z';
  1 while $str =~ s/$chars//;
  $str
}

printf "%s\n",good_string('WeEeekly');
printf "%s\n",good_string('abBAdD');
printf "%s\n",good_string('abc');