use strict;
use warnings;
use Data::Dump qw( dd );

sub _collapse {
  my $tree = shift;
  my ( $stree, $append );

  if ( ref $tree ) {
    my @keys = keys %$tree;
    if ( @keys == 1 and $keys[0] ne '' ) {
      ( $stree, $append ) = _collapse( $tree->{ $keys[0] } );
      return $stree, defined $append ? $keys[0] . $append : $keys[0];
    }
    else {
      for (@keys) {
        ( my $ref, $append ) = _collapse( $tree->{$_} );
        $stree->{ defined $append ? $_ . $append : $_ } = $ref;
      }
      return $stree;
    }
  }
  return;
}

sub collapse {
  my $ctree = shift;
  my ( $stree, $append ) = _collapse($ctree);
  if ( defined $append ) {
    return { $append => $stree };
  }
  else {
    return $stree;
  }
}

sub shorten {
  my $stree = shift;
  my $limit = shift;

  if ( ref $stree ) {
    while ( my ( $k, $v ) = each %$stree ) {
      local our @parts = @parts;
      push @parts, $k if $k ne '';
      if ( $k eq '' ) {
        if ( @parts > $limit ) {
          print "!\n";
          next;
        }
        my $remaining = $limit - @parts;
        my $shortened = '';
        for ( 0 .. $#parts ) {
          $shortened .= substr $parts[$_], 0, 1;
          my $str = substr $parts[$_], 1, $remaining;
          $shortened .= $str;
          last if ( ( $remaining -= length $str ) < 0 );
        }
        print $shortened, "\t", join( '', @parts ), "\n";
      }
      shorten( $v, $limit );
    }
  }
}

my $ctree = {};

while (<DATA>) {
  chomp;
  my $ref = $ctree;
  for ( split // ) {
    no warnings 'void';
    $ref->{$_}->{''}; # looks like a decent autovivification bug ;-)
    $ref = $ref->{$_};
  }
  $ref->{''} = undef;
}

#dd $ctree;
my $stree = collapse($ctree);
#dd $stree;
shorten( $stree => 5 );

__DATA__
A2990_duallayer_1
A2990_duallayer_2
A2990_duallayer_3
A2990_duallayer_4
A2990_duallayer_5
A2990_duallayer_6
A2990_duallayer_7
A2990_duallayer_8
A2990_duallayer_9
A2990_duallayer_10
LXP_01
LXP_02
LXP_03
LXP_04
LXP_05
LXP_06
LXP_07
LXP_08
LXP_09
LXP_10
LXP_11
LXP_12
LXP_13
LXP_14
LXP_15
LXP_16
LXP_17
LXP_18
Normal_1
Normal_2
Normal_3
Normal_4
Normal_5
Normal_6
Lenoc3_carina_A
Lenoc3_carina_B
Lenoc3_carina_C
Lenoc3_duallayer_1
Lenoc3_duallayer_2
Lenoc3_duallayer_3
Lenoc5_carina_1
Lenoc5_carina_2
Lenoc5_carina_3
Lenoc5_duallayer_1
Lenoc5_duallayer_2
Lenoc5_duallayer_3