faster implementation of sum ( for Codility test )

Question

How can the following simple implementation of sum be faster?

private long sum( int [] a, int begin, int end ) {
    if( a == null   ) {
        ret         


        

Answer 1

Some tips:

• Use a profiler to identify where you're spending a lot of time.

• Write good performance tests so that you can tell the exact effect of every single change you make. Keep careful notes.

• If it turns out that the bottleneck is the checks to ensure that you're dereferencing a legal address inside the array, and you can guarantee that begin and end are in fact both inside the array, then consider fixing the array, making a pointer to the array, and doing the algorithm in pointers rather than arrays. Pointers are unsafe; they do not spend any time checking to make sure you're still inside the array, so therefore they can be somewhat faster. But you take responsibility then for ensuring that you do not corrupt every byte of memory in the address space.