use strict;
use Data::Dumper;

my @input = ("1 2 3",
             "5 5 6",
             "1 4 6"
            );

# outer map: take each input line
# inner map: split it on white space and return it as a hash ref
my @array = map { 
                 { map { $_ => 1 } split(/\s+/,$_) }
                } @input;

print Dumper @array;

my %unique;
for (my $i=0; $i<=$#array; $i++) {
        foreach (keys %{$array[$i]}) {
                $unique{$_}->{'pos'}->{$i} = 1;
                $unique{$_}->{'count'}++;
        }
}

my @duplicates =  grep { $unique{$_}->{'count'} > 1 } keys %unique;

foreach (@duplicates) {
        print "DUP: $_ In lists: ";

        print join(",",keys %{$unique{$_}->{'pos'}});

        print "\n";
}