#!/usr/bin/perl
## LONGEST COMMON SUBSTRINGs (LCS):  
use warnings;
use strict;
sub lc_substr {
  my ($str1, $str2) = @_; 
  my $l_length = 0; # length of longest common substring
  my $len1 = length $str1; 
  my $len2 = length $str2; 
  my @char1 = (undef, split(//, $str1)); # $str1 as array of chars, indexed from 1
  my @char2 = (undef, split(//, $str2)); # $str2 as array of chars, indexed from 1
  my @lc_suffix; # "longest common suffix" table
  my @substrings; # list of common substrings of length $l_length 
  for my $n1 ( 1 .. $len1 ) { 
    for my $n2 ( 1 .. $len2 ) { 
      if ($char1[$n1] eq $char2[$n2]) {
        # We have found a matching character. Is this the first matching character, or a
        # continuation of previous matching characters? If the former, then the length of
        # the previous matching portion is undefined; set to zero.
        $lc_suffix[$n1-1][$n2-1] ||= 0;
        # In either case, declare the match to be one character longer than the match of
        # characters preceding this character.
        $lc_suffix[$n1][$n2] = $lc_suffix[$n1-1][$n2-1] + 1;
        # If the resulting substring is longer than our previously recorded max length ...
        if ($lc_suffix[$n1][$n2] > $l_length) {
          # ... we record its length as our new max length ...
          $l_length = $lc_suffix[$n1][$n2];
          # ... and clear our result list of shorter substrings.
          @substrings = ();
        }
        # If this substring is equal to our longest ...
        if ($lc_suffix[$n1][$n2] == $l_length) {
          # ... add it to our list of solutions.
          push @substrings, substr($str1, ($n1-$l_length), $l_length);
        }
      }
    }
  }   
 
  return @substrings;
}
my @result1=lc_substr qw(ABABC BABCA ABCBA);
my $result1=join('',@result1);
my $leng1=length($result1); 
print"\n The longest common substring :\n";
print "\n@result1: Length=$leng1 letters\n";
print"\n Other common substrings in order of decreasing lengths are:\n";
my @result2="?";

##</code><code>##

The longest common substring :
BABC: Length=4 letters
Other common substrings in order of decreasing lengths are:??

##</code><code>##

The longest common substring :
ABC; Length=3
Other common substrings in order of decreasing lengths are:
AB: Length=2
BC: Length=2
BA: Length=2

##</code><code>##

#!/usr/bin/perl
## LONGEST COMMON SUBSTRINGS (sorted) from a set of given sequences:
use strict;
use warnings;
sub LCS {                             # Line 5 
    my ($ctx, $a, $b) = @_;
    my ($amin, $amax, $bmin, $bmax) = (0, $#$a, 0, $#$b);
    while ($amin <= $amax and $bmin <= $bmax and $a->[$amin] eq $b->[$bmin]) {
        $amin++;
        $bmin++;
    }
    while ($amin <= $amax and $bmin <= $bmax and $a->[$amax] eq $b->[$bmax]) {
        $amax--;
        $bmax--;
    }                                  # Line 15 
    my $h = $ctx->line_map(@$b[$bmin..$bmax]); # line numbers are off by $bmin
    return $amin + _core_loop($ctx, $a, $amin, $amax, $h) + ($#$a - $amax)
        unless wantarray;
    my @lcs = _core_loop($ctx,$a,$amin,$amax,$h);
    if ($bmin > 0) {                   # Line 20 
        $_->[1] += $bmin for @lcs; # correct line numbers
    }
    map([$_ => $_], 0 .. ($amin-1)),
        @lcs,
            map([$_ => ++$bmax], ($amax+1) .. $#$a);
    }
sub a {                                    
    my $match = CSS(@_);            # line 28 
    if ( ref $_[0] eq 'ARRAY' ) {
       @$match = map{$_->[0]}sort{$b->[1]<=>$a->[1]}map{[$_,scalar(@$_)]}@$match
    }
    else {                          # Line 32 
       @$match = map{$_->[0]}sort{$b->[1]<=>$a->[1]}map{[$_,length($_)]}@$match
    }
  return $match;
}
## Data Input & Results:                   # Line 37 
print"\nThe longest common substrings in decreasing order of lengths:\n";
my $result1=a qw(ABABC BABCA ABCBA);
my $leng1=$result1;                        # Line 40 
print"\n$result1; Length=$leng1\n\n";
exit;

##</code><code>##

Microsoft Windows [Version 6.1.7600]
Copyright (c) 2009 Microsoft Corporation.  All rights reserved.
C:\Users\x>cd desktop
C:\Users\x\Desktop>try1.pl

The longest common substrings in decreasing order of lengths:
Undefined subroutine &main::CSS called at C:\Users\DR-SUPRIYO\Desktop\try1.pl line 28.
C:\Users\x\Desktop>