use strict;
use warnings;

sub get_output {
    my ($source,$pair) = @_;
    
    my @sorted_src = sort {$a <=> $b} (@{$source});
    my @sorted_pr = sort {$a <=> $b} (@{$pair});
    
    my @output;
    foreach my $sc (@sorted_src) {
        foreach my $pr (@sorted_pr) {
            last if ($pr == $sc);
            push(@output,($sc)) if ($sc < $pr);
        }
    }
    my %temp_hash = map {$_, 1} @output;
    @output = keys %temp_hash;
    @output = sort {$a <=> $b} (@output);
    return @output;
}

my @source = (1,2,3,4);
my @pair = (1,2);
my @pair2 = (2,3);
my @pair3 = (1,3);
my @pair4 = (2,4);

my @result;

@result = get_output(\@source,\@pair);
print "Input list:  ";
print "@pair\n";
print "Result list:  ";
print "@result\n\n";
undef @result;

@result = get_output(\@source,\@pair2);
print "Input list:  ";
print "@pair2\n";
print "Result list:  ";
print "@result\n\n";
undef @result;

@result = get_output(\@source,\@pair3);
print "Input list:  ";
print "@pair3\n";
print "Result list:  ";
print "@result\n\n";
undef @result;

@result = get_output(\@source,\@pair4);
print "Input list:  ";
print "@pair4\n";
print "Result list:  ";
print "@result\n\n";
undef @result;
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