INPUT data:
R00009MM#R00009#2 C00027MM <=> C00007MM + 2 C00001MM
R00014MM#R00014#C00022MM + C00068MM + C00080MM <=> C05125MM + C00011MM
R00081MM#R00081#C00007MM + 4 C00126MM + 8 C00080MM <=> 4 C00125MM + 2 C00001MM + 4 C00080Cyto
R00086MM#R00086#C00008MM + C00009MM + 7 C00080Cyto <=> C00002MM + C00001MM + 7 C00080MM
R00094MM#R00094#2 C00051MM + C00003MM <=> C00127MM + C00004MM + C00080MM

##</code><code>##

OUTPUT expected.
R00081MM -> R00094MM
R00014MM -> R00086MM
R00081MM -> R00086MM
R00086MM -> R00081MM
R00094MM -> R00014MM
R00009MM -> R00081MM


##</code><code>##

#!/usr/bin/perl
use warnings;
use strict;
open (IN, "input.txt") || die $!;
#open (OUT,">output.txt") || die $!;

my %groups;
my @rxnGraph;
while (<IN>) {
    chomp $_;
    my @rxn = split /#/, $_;
    next if length $rxn[1] == 0;
    my ($left_side, $right_side) = split /\s*<=>\s*/, $rxn[2];
    
    my @left_els = split /\s*\+\s*/, $left_side;
    my @right_els = split /\s*\+\s*/, $right_side;
    my $x=0;
    for ($x=0; $x<=$#left_els; $x++){
        $left_els[$x]=~s/^[0-9]//;
        if($left_els[$x]=~/C.*/){
        #print ">>",$left_els[$x],"\n"
        }
    }
   #     print ">L>@left_els\n";
    my $y=0;
    for ($y=0; $y<=$#right_els; $y++){
        $right_els[$y]=~s/^[0-9]//;
        if($right_els[$y]=~/C.*/){
  #      print ">>>$right_els[$y]\n";
        }
    }
 #   print ">R>@right_els\n";
    $groups{$_}{left}  = $rxn[0] for @left_els;
    $groups{$_}{right}  = $rxn[0] for @right_els;   
}
#while( my ($keys, $values) = each(%groups)){
    #print ">>K>>>$keys\n";
    #}
for my $grp (keys %groups) {
    if (2 == grep exists $groups{$grp}{$_}, qw/left right/) {
        print "$groups{$grp}{right} ->",
                           " $groups{$grp}{left}\n";
       # push @rxnGraph, "$groups{$grp}{right},",
        #                   " $groups{$grp}{left}\n";
                           
         }
    }
#print OUT @rxnGraph;