I'm not sure I understand your problem, but my guess goes something like this: 

#!/usr/bin/perl

use strict; # https://perlmonks.org/?node_id=11152381
use warnings;

my %sets = ( A => [1,2,3], B => [3, 4], C => [1, 3, 4] );
use Data::Dump 'dd'; dd 'original sets', \%sets;

my %intersection;
for my $setname ( keys %sets )
  {
  $intersection{$_}{$setname}++ for @{ $sets{$setname} };
  }
use Data::Dump 'dd'; dd 'intersection', \%intersection;

print "items in more than one set:\n";
for my $setname ( sort keys %intersection )
  {
  if( 1 < keys %{ $intersection{$setname} } )
    {
    my $where = join ' and ', map "'$_'",
      sort keys %{ $intersection{$setname} };
    print "    '$setname' is in $where\n";
    }
  }

[download]

Outputs (complete with intermediate calculations): 

(
  "original sets",
  { A => [1, 2, 3], B => [3, 4], C => [1, 3, 4] },
)
(
  "intersection",
  {
    1 => { A => 1, C => 1 },
    2 => { A => 1 },
    3 => { A => 1, B => 1, C => 1 },
    4 => { B => 1, C => 1 },
  },
)
items in more than one set:
    '1' is in 'A' and 'C'
    '3' is in 'A' and 'B' and 'C'
    '4' is in 'B' and 'C'

[download]

In reply to Re: Set intersection problem by tybalt89
in thread Set intersection problem by baxy77bax

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.