use strict;
use warnings;

use Data::Dumper;

my $str1 = 'Perlmonks is the best perl community';
my $str2 = 'Perlmonks is one of the best community of perl users';

if ( $str1 eq $str2 ) {
	print "$str1\n$str2\n";
	exit;
}

my @wl1 = split /\s+/, $str1;
my @wl2 = split /\s+/, $str2;
my $diff_str1 = '';
my $diff_str2 = '';
my %wc1;
my %wc2;

foreach my $word (@wl1) {
	$wc1{$word}++;
}

foreach my $word (@wl2) {
	$wc2{$word}++;
}

while (@wl1 || @wl2) {
	my $word1 = '';
	my $word2 = '';
	# being sloppy and not decrementing word counts for new words
	# since we only use them for moves
	while (!$wc2{$word1}) { 
		$diff_str1 .= "<$word1> " if $word1;
		$wc1{$word1}-- if $word1;
		$word1 = ''; # prevent fall through if this is the last word
		last if !@wl1;
		$word1 = shift @wl1;
	}

	while (!$wc1{$word2}) { 
		$diff_str2 .= "<$word2> " if $word2;
		$wc2{$word2}-- if $word2;
		$word2 = ''; 
		last if !@wl2;
		$word2 = shift @wl2;
	}

	if ( $word1 && $word2 && $word1 eq $word2 ) {
		$diff_str1 .= $word1 . ' ';    # pairing the word from the origional string with it's output
		$diff_str2 .= $word2 . ' ';    # lets us do things like case insensitive, but preserving match later
	}

	else {
		$diff_str1 .= "[$word1] " if $word1;
		$diff_str2 .= "[$word2] " if $word2;
	}
	$wc1{$word2}--;
	$wc2{$word1}--;
}

print "$diff_str1\n$diff_str2\n";

##</code><code>##

Perlmonks is the best [perl] [community]
Perlmonks is <one> <of> the best [community] <of> [perl] <users>

##</code><code>##

$str1 = 'Perlmonks is the best perl perl community';
$str2 = 'Perlmonks is one of the best community of perl users';
---------
Perlmonks is the best [perl] <perl> [community]
Perlmonks is <one> <of> the best [community] <of> [perl] <users>