快速幂

public class Solution {
    public double Power(double base, int exponent) {
        double res = 1;
        if(exponent < 0) {
            exponent *= -1;
            base = 1 / base;
        }
        while(exponent != 0) {
            int u = exponent & 1;
            if(u == 1) {
                res *= base;
            }
            base *= base;
            exponent >>>= 1;
        }
        return res;
  }
}