#!/usr/bin/perl
use strict;
use warnings;
use 5.10.0;

my $seq = 'deabcdefabcdefgAbcdeabcdefabcdefgAbcdeabcdefabcdefgAbcdeabcdefabcdefgAbcdeabcdefabcdefgAbcdeabcdefabcdefg';
my %val = do{my $cnt = 0; map {$_ => ++$cnt} split //, 'Aabcdefg'};

my $xor = 0;
my $loop = 0;
for (split //, $seq) {
    $loop++;
    $xor ^= $val{$_};
    say $loop if !$xor;
}

##</code><code>##

9
36
45
72
81

##</code><code>##

my %val = do{my $cnt = 0; map {$_ => 2**(++$cnt)} split //, 'Aabcdefg'};