use strict;
use warnings;

use Data::Dumper;

my @arr;
push @arr
   , ( q{A} .. q{Z}, q{0} .. q{9} )[ int rand 36 ]
   . sprintf( q{%04d}, int rand 10000 )
   for 1 .. 25;

print Data::Dumper
   ->Dumpxs( [ \ @arr ], [ qw{ *arr } ] );

my %letters = ();
foreach my $letter ( q{A} .. q{Z} )
{
    last unless @arr;
    my $rxLetter = qr{$letter};
    foreach my $idx ( reverse 0 .. $#arr )
    {
        next unless $arr[ $idx ] =~ $rxLetter;
        push @{ $letters{ $letter } }, splice @arr, $idx, 1;
    }
}

print Data::Dumper
   ->new( [ \ %letters, \ @arr ], [ qw{ *letters *arr } ] )
   ->Sortkeys( 1 )
   ->Dumpxs();