Answer for http://codility.com/test/c/demoUNSPD5-BS3/

Solution.java

// you can also use imports, for example:
// import java.math.*;
class Solution {
  public int equi ( int[] A ) {
    if (A.length == 0) return -1;
        
        long[] sum = new long[A.length];
        sum[0] = A[0];
        for (int i = 1; i < A.length; i++) {
            sum[i] = sum[i - 1] + A[i];
        }
        
        for (int i = 0; i < A.length; i++) {
            if ((sum[i] - A[i]) == sum[A.length - 1] - sum[i]) {
                return i;
            }
        }
        
        return -1;
  }
}