TIMTOWTDI

• Sort both arrays
• take the first element from array1 and starting at the top of array2 move down until either you find the same element in array2 (in which case you continue with the next element of array1) or reach an element which is larger than the element your were checking against (in which case you have found an element in array 1 which is not in array 2)

The maximum number of comparisons would be the length of array1 + array2. Of course you have the overhead of the sorting to take into account, put perhaps you are lucky and they are sorted to start with (such as when they are the result of a database select).

CountZero

"If you have four groups working on a compiler, you'll get a 4-pass compiler." - Conway's Law