I've been struggling to find a non-recursive solution to this, but alas, I have hit the wall. I'm simply trying to loop through all the string combinations from '000' to 'zzzzzzzzzzzzzzzz'. The following code seems to work just fine, but I have a feeling that it'll get ugly once it's dealing with longer and longer strings, hence why I'm looking for the recursion-less fix. If nothing else, I guess I can wrap this up into a package to keep the calling code cleaner. Anyway, here it is:

#!/usr/bin/perl -w
use strict;

my $number = '000';

do {
    increment( \$number );
    print "$number\n";
} until $number eq 'zzzzzzzzzzzzzzzz'; # or some other long string

sub increment {

    my ( $number_ref ) = @_;
    my @digits = split //, $$number_ref;

    unshift @digits, undef while @digits < 16;
    _increment_digit( \@digits, scalar @digits - 1 );

    $$number_ref = join '', grep { defined } @digits;

}

sub _increment_digit {

    my ( $array_ref, $index ) = @_;

    if ( ! defined $array_ref->[$index] ) {
        $array_ref->[$index] = 0;
    }
    elsif ( $array_ref->[$index] ge '0' && $array_ref->[$index] lt '9'
+ ) {
        $array_ref->[$index]++;
    }
    elsif ( $array_ref->[$index] eq '9' ) {
        $array_ref->[$index] = 'a';
    }
    elsif ( $array_ref->[$index] ge 'a' && $array_ref->[$index] lt 'z'
+ ) {
        $array_ref->[$index] = chr( ord( $array_ref->[$index] ) + 1 );
    }
    elsif ( $array_ref->[$index] eq 'z' ) {
        $array_ref->[$index] = 0;
        _increment_digit( $array_ref, ($index - 1) );
    }

}

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In reply to Iterating through string combinations by patgas

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