数值的整数次方

https://www.nowcoder.com/practice/1a834e5e3e1a4b7ba251417554e07c00

逐项相乘

public static double Power(double base, int exponent) {
    //保证不同时为0，先处理各自为0的情况
    if (exponent == 0) return 1.0;
    if (base == 0.0) return 0.0;
    double ans = 1.0;
    if (exponent < 0) {
        base = 1 / base;
        exponent = (-1) * exponent;
    }
    for (int i = 0; i < exponent; i++) {
        ans *= base;
    }
    return ans;
}