Or maybe you want to just skip single elements, without caring if you end up with pairs or not.

@array1 = qw(1 1 5 3);
@array2 = qw(4 5 6 1);

my %lookup;

sub filter {
   return 0 if $lookup{$_};
   $lookup{$_} = 1;
   return 1;
}

@array1 = grep filter, @array1;
@array2 = grep filter, @array2;

print('@array1 = (', join(', ', @array1), ")\n");  # 1, 5, 3
print('@array2 = (', join(', ', @array2), ")\n");  # 4, 6
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