class Ideone
{
 
	public static  double sum(double [] a, int low, int high) throws Exception{
        if(low > high){
            throw new IllegalArgumentException();
        }
        else if(low == high){
            return a[low];
        }
        return sum(a, low, (low+high)/2) + sum(a, (low+high)/2+1, high);
    }
 
    public static void main(String[] args) throws Exception {
        double[] arr = { 0, 1, 2, 3, 4 };
 
        System.out.println(sum(arr, 1, 3)); // 6
    }
}

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