#!/usr/bin/perl

use strict; 
use warnings;

use Data::Printer;


my @a = (1,2,3,4);
my @b = (1,3,2,5,6);
p(@a);
p(@b);
my %h = map { $_ => 1 } @a;
p(%h);
@b = grep { ! exists $h{$_} } @b;
p(@a);
p(@b);

__END__
ergibt:

[
    [0] 1,
    [1] 2,
    [2] 3,
    [3] 4
]
[
    [0] 1,
    [1] 3,
    [2] 2,
    [3] 5,
    [4] 6
]

{
    1   1,
    2   1,
    3   1,
    4   1
}

[
    [0] 1,
    [1] 2,
    [2] 3,
    [3] 4
]
[
    [0] 5,
    [1] 6
]