public class commonAlgorithm {

    /**
     * 
     *
     * @param num
     * @return
     */
    private static boolean isPrime(int num) {

        if (num = arr.length)
            throw new IllegalArgumentException("j is out of bound.");

        Object temp = arr[i];
        arr[i] = arr[j];
        arr[j] = temp;
    }

    /**
     * n
     *
     * @param n
     * @return
     */
    private static int sum(int n) {

        if (n < 0)
            throw new IllegalArgumentException("n should be greater or equal to zero.");

        int ret = 0;
        for (int i = 0; i  0)
                l = mid + 1;  // target[mid+1...r); [l...mid]target
            else    // target < arr[mid]
                r = mid;  // target[l...mid); [mid...r)target
        }
        return -1;
    }


}