astro86 has asked for the wisdom of the Perl Monks concerning the following question:

Hello Monks! I need your help on this one as it's been driving me nuts for the last few days. Please note that I have simplified things a bit, but I have a strings that look like this:
A B _ B A A A

I need to find all the unique ways I can remove, in order, the tokens contained in:
A B A

Such that I get the following results, where the 'X' is a removed token from my token string: X X _ B X A A
X X _ B A X A
X X _ B A A X
X B _ X X A A
X B _ X A X A
X B _ X A A X

Which yields 2 unique paths these can be removed:
B _ A A
_ B A A

Any help or hints on how to accomplish this would be very helpful.
Thank you.

Replies are listed 'Best First'.
Re: Finding unique deletion strings
by Anonymous Monk on Sep 08, 2016 at 02:56 UTC 
    #!/usr/bin/perl -l

# http://perlmonks.org/?node_id=1171353

use strict;
use warnings;

my $have = 'A B _ B A A A';
my $remove = 'A B A';
my @left;
my %left;

my $pattern = $remove =~ s/ /(.*)/gr;

$have =~ /^$pattern$(?{ push @left, "$`$1$2$'" })(*FAIL)/;

s/  +/ /g, s/^ //, s/ $//, $left{$_}++ for @left;

print for sort keys %left;

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[d/l]
      That was fast and spot on! Well done and thank you!
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