use strict;
use warnings;
use Algorithm::Diff qw/LCSidx/;

my $str1 = "I am trying to find a perl LCS module in perl monk";
my $str2 = "perl monk";

print longest( $str1, $str2 );

sub longest {
    my @seq1 = split /\s+/, $_[0];
    my @seq2 = split /\s+/, $_[1];
    my ( $idx1, $idx2 ) = LCSidx( \@seq1, \@seq2 );
    my @list = @seq1[@$idx1];
    return join( ' ', @list ), '[', join( ',', @$idx1 ), ']';
}