16. 数值的整数次方

public double Power(double x, int n) {
    boolean isNegative = false;
    if (n < 0) {
        n = -n;
        isNegative = true;
    }
    double res = pow(x, n);
    return isNegative ? 1 / res : res;
}

private double pow(double x, int n) {
    if (n == 0) return 1;
    if (n == 1) return x;
    double res = pow(x, n / 2);
    res = res * res;
    if (n % 2 != 0) res *= x;
    return res;
}