#!/usr/bin/perl -w
use strict;
use warnings;
open(IN,"<",$ARGV[0]) or die $!;
my %hash1;
my %hash2;
my @head;
$/=">";
while (<IN>){
chomp;
next if (/^$/);
my ($head,$seq)=split /\n/,$_;
$seq=~s/\n//g;
my $start=substr($seq,0,3);
my $end=substr($seq,-3,3);
$hash1{$head}=$start;
$hash2{$head}=$end;
push @head,$head;
}
my %hash3;
for my $head(@head){
for my $head1(@head){
next if ($head eq $head1);
if ($hash2{$head} eq $hash1{$head1}){
$hash3{$head}{$head1}=0;
}
if ($hash2{$head1} eq $hash1{$head}){
$hash3{$head1}{$head}=0;
}
}
}
for my $key(keys %hash3){
for my $key1(keys %{$hash3{$key}}){
print $key,"\t",$key1,"\n";
}
}