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

I don't believe the problem is in the code you provided, but somehow the bigger solution must be suboptimal. This code looks good for calculating the sum of one slice of the array, but maybe it's not what you need to solve the whole problem.