Question

i’ve got two lists A and B, B = A + C – D. All elements are unique, no duplicates. How do i get the lists of:
(1) the new items added, C
(2) the old items removed, D

C and D aren’t more than 10000 elements or so.

Edit

Crap, sorry guys – forgot the important detail – these are both text files, not in memory elements.

Answer 1

You said you already have two files A and B.

Here’s the easiest, fastest solution assuming you’re running on a Unix system.

system("comm -13 A B > C");
system("comm -23 A B > D");

//read C and D in PHP