Help with an algorithm!

[MGW via Digitalmars-d-learn]

There are two arrays of string [] mas1, mas2; Size of each about 
5M lines. By the size they different, but lines in both match for 
95%. It is necessary to find all lines in an array of mas2 which 
differ from mas1. The principal criterion - speed. There are the 
8th core processor and it is good to involve a multithreading.