my @A = (1,3,4,5,6,8); 
my @B = (1,3,5,7,9);

my (%A, %B, @C);

@A{@A} = (1) x @A; 
@B{@B} = (1) x @B; 
@C = grep { delete $B{$_} && delete $A{$_} } sort keys %A;
@A = sort keys %A; 
@B = sort keys %B;