How to tell if a string can be transformed into another string by removing or uppercasing lowercase letters? - perl

Question

In perl, I have two input strings, for this example, ahueFFggLKy and HFFGLK. I want to be able to iterate through all of the possible combinations of my input without lowercase letter groups (a, h, u, e, g...ah, au...hegy, etc) so in each iteration lowercase letters are removed and the remaining lowercase letters are uppercased:
ah:
ueFFggLKy (UEFFGGLKY)
^^
au:
h eFFggLKy (HEFFGGLKY)
^ ^
hegy:
a u FF gLKy | a u FFg LKy (AUFFGLKY)
^ ^ ^ | ^ ^ ^
auegy:
h FF gLK | h FFg LK (HFFGLK)
^ ^^ ^ ^ ^ ^^ ^ ^ -^--^-
The last option (auegy) is the answer, and I want to be able to iterate over letters to determine if I am able to convert ahueFFggLKy to HFFGLK without modifying any of the capital letters. This example would return "YES".
If inputs like fOoBar and BAR come up, I am not successfully able to convert fOoBar to BAR because the O in fOoBar is capitalized. My program would return "NO".
Can someone provide me with a perl example of how this would be done?

Answer 1

I think I have understood your requirement: the first string may be transformed by either deleting or upper-casing any lower-case letter, and you wish to know whether the second string can be derived from the first in this way
I suggest that you can transform the second string to a regex pattern to achieve this. If every upper-case letter in the second string must be matched by the corresponding upper or lower-case letter in the first, with any number of intervening lower-case letters, then the transformation is possible. Otherwise it is not
This program implements the idea
use strict;
use warnings 'all';
use feature 'say';
my #pairs = (
[ qw/ ahueFFggLKy HFFGLK / ],
[ qw/ fOoBar BAR / ],
);
for my $pair ( #pairs ) {
my ($s1, $s2) = #$pair;
printf "%s => %s -- %s\n", $s1, $s2, contains($s1, $s2) ? 'YES' : 'NO';
}
sub contains {
my ($s1, $s2) = #_;
my $re = join ' \p{Ll}* ', map { "(?i: $_ )" } $s2 =~ /\p{Lu}/g;
$re = qr/ ^ \p{Ll}* $re \p{Ll}* $ /x;
$s1 =~ $re;
}
output
ahueFFggLKy => HFFGLK -- YES
fOoBar => BAR -- NO
To read an array like #pairs from STDIN you could write something like this
my #pairs;
{
local $/;
my #input = split ' ', <>;
push #pairs, [ splice #input, 0, 2 ] while #input > 1;
}

Answer 2

Kind of unelegant solution, but it seems to output what you need.
#!/usr/bin/perl
use warnings;
use strict;
use List::Util qw{ all };
my ($str1, $str2) = qw( ahueFFggLKy HFFGLK );
my #small_indices;
push #small_indices, pos($str1) - 1 while $str1 =~ /[[:lower:]]/g;
my #present = (0) x #small_indices;
until (all { $_ } #present) {
my $try = $str1;
for my $i (reverse 0 .. $#present) {
substr $try, $small_indices[$i], 1,
$present[$i] ? substr $str1, $small_indices[$i], 1
: q();
}
if (uc $try eq $str2) {
print $present[$_] ? q() : substr $str1, $small_indices[$_], 1
for 0 .. $#present;
print ":\n";
my $j = 0;
for my $i (0 .. length($str1) - 1) {
my $char = substr $str1, $i, 1;
if ($char eq uc $char || $present[$j++]) {
print $char;
} else {
print '.';
}
}
print "\n";
}
my $idx = 0;
$present[$idx] = 0, ++$idx while $present[$idx];
$present[$idx] = 1;
}
It builds an indicator function #present, which say what lowercase letters are present in the string. All possible values of #present are iterated by adding 1 to the binary number corresponding to the function.