#!usr/bin/perl
use strict; use warnings; use Data::Dumper;

my @key_array = 'a' .. 'z';
my @set_array = ( ['a', 'b'],  ['e','f'], ['f','g'],['x','y'] );

# {a =>{a=>1}, b=>{b=>1}, ....}
my %set = map {$_ => {$_ => 't'}} @key_array;  

for my $s (@set_array) {
	@{$set{$_}}{@$s} = (1) x @$s for @$s;	
=my_memo	
	#same as ...
	for (@$s){
      	    @{$set{$_}}{@$s} = (1) x @$s 
	}
	#fill hash value at one time
	my %h; @h{ 1 .. 5 }= 'A' ..'F';  
	
	#(1) x @$s 
	if @$s === (a,b) ,  (1) x @$s === (1,1) 
     
    #vertex which has edge information ..
    #{ a=>{a=>1,b=>1}, b=>{a=>1,b=>1} ...
=cut 
}

my $saw = '';

print map "$_\n",									
	  grep $saw =~ s/^(?!.*$_)/$_ /,				
=my_memo
     # ??? how it can remove duplicate like "a,b","a,b" or "e,f,g","e,f","f,g"
    
     here comes "e,f,g", $saw='',     	==> $saw="e,f,g"		==> true  #saw doesn't have "" replace ^ to "e,f,g"
			    "a,b"    $saw="e,f,g" 	==> $saw="a,be,f,g"     ==> true  #saw doesn't have "a,b", replace ^ to "a,b
			    "a,b"    $saw="a,be,f,g" 	==> $saw="a,be,f,g"     ==> false #saw have "a,b" not match;
			    "e,f"    $saw="a,be,f,g" 	==> $saw="a,be,f,g"     ==> false #saw have "e,f" not match;
      ... removes edge already seen ... really great.
=cut
      sort {length $b <=> length $a || $a cmp $b}	  #sort by length desc || a cmp b
      map join(',', sort keys %$_),					#"a,b" ... sorted  
      values %set;					 				# values => {a=>1,b=>1}, {a=>1,b=>1},{c=>1},{d=>1},,,