#!/usr/bin/perl

# http://perlmonks.org/?node_id=1202179

use strict;
use warnings;

use Data::Dumper;

chomp( my @words = <DATA> );

# find the "banks" in the word list

my %banks = map { $_, [ ] } grep !/(.).*\1/, @words;
print Data::Dumper->Dumpxs( [ \ @words, \ %banks ], [ qw{ *words *banks } ] );

# find what a word "banks" to and save if "bank" exists

for ( @words )
  {
  my $banksto = tr///csr;
  print qq{$_ -> $banksto\n};
  exists $banks{$banksto} and push @{ $banks{$banksto} }, $_;
  }

print "@$_\n" for values %banks;

__DATA__
ab
aabb
aaabbb
aaabbab
xxyy
xxxyyy