#!/usr/bin/perl

use strict;
use warnings;

use Data::Dumper;

#  Build all possible strings based on the following three rules:
#  1. Start with 'foobar'
#  2. Optionally include first set:
#     a. zero or one 'a';
#     b. zero or one 'b'; and
#     c. zero or one 'c'.
#  3. Optionally include second set:
#     a. 'X'
#     b. zero or one 'a';
#     c. zero or one 'b'; and
#     d. zero or one 'c'.

my ( @w, %solutions );

{
  @w = ('foobar');
  for my $firstSet ( 0 .. 1 ) {
    for my $a1 ( 0 .. 1 ) {
      for my $b1 ( 0 .. 1 ) {
        for my $c1 ( 0 .. 1 ) {
          for my $secondSet ( 0 .. 1 ) {
            for my $a2 ( 0 .. 1 ) {
              for my $b2 ( 0 .. 1 ) {
                for my $c2 ( 0 .. 1 ) {
                  if ($firstSet) {
                    if ($a1) { addThisChar('a'); }
                    if ($b1) { addThisChar('b'); }
                    if ($c1) { addThisChar('c'); }
                  }
                  if ($secondSet) {
                    addThisChar('X');
                    if ($a2) { addThisChar('a'); }
                    if ($b2) { addThisChar('b'); }
                    if ($c2) { addThisChar('c'); }
                  }
                  saveThatPattern();
                }
              }
            }
          }
        }
      }
    }

  }
  for my $key (
    sort { $solutions{$b} <=> $solutions{$a} }
    sort keys %solutions
    )
  {
    print "  $key => $solutions{ $key }\n";
  }
}

sub addThisChar { push( @w, shift ); }
sub saveThatPattern { $solutions{ join( '', @w ) }++; @w = ('foobar'); }