#!/usr/bin/perl

use strict; # https://perlmonks.org/?node_id=11118150
use warnings;

while( <DATA> )
  {
  my @sizes = split ' ', <DATA>;
  my $regex = join '', map { "(?=(.))(\\g{-2}{$_})\\g{-2}*.*?" } @sizes;
  my @groups = ( /$regex/ )[ map 2 * $_ + 1, 0 .. $#sizes ];
  print "[@groups]\n";
  }

__DATA__
cbaa
1 2
cba
1
bbaa
1 2
cccqrrtaaa
2 2 2
cccqrrtaaa
1 1 2 2
cccqrrtaaa
1 1 1 1 3

##</code><code>##

[c aa]
[c]
[b aa]
[cc rr aa]
[c q rr aa]
[c q r t aaa]