Codility solution https://codility.com/demo/results/demoGYMPA6-Q73/ Take your own here: https://codility.com/demo/take-sample-test/ This is a demo task. You can read about this task and its solutions in this blog post: http://dev.tasubo.com/2012/09/tips-for-tasks-on-codility.html

Solution.java

class Solution {
    public int solution(int[] A) {
        long left = 0;
        long right = 0;
        long sum = sum(A);
        
        for (int i = 0; i < A.length; i++) {
            right = sum - left - A[i];
            
            if (left == right) 
                return i;
            
            left += A[i];
        }
        
        return -1;
    }
    
    private long sum(int[] A) {
        long sum = 0;
        
        for (int i = 0; i < A.length; i++) {
            sum += A[i];
        }
        
        return sum;
    }
}