直接循环累乘

思路就是暴力累乘：

    public class Solution {

        public double Power(double base, int exponent) {
            if (base == 0.0) {
                return base;
            }
            double sum = 1.0d;
            int n = exponent > 0 ? exponent : -exponent;
            while (n > 0) {
                sum = sum * base;
                n = n - 1;
            }
            return exponent > 0 ? sum : 1 / sum;
        }
    }