题目描述
给定一个double类型的浮点数base和int类型的整数exponent。求base的exponent次方。

public class Solution {
    public double Power(double base, int exponent) {
        if(exponent == 0){
            return 1;
        }
        if(exponent == 1){
            return base;
        }
        double ret = 0;
        if(exponent > 0){
            //奇数
            if(exponent%2!=0){
                double tmp = Power(base,exponent/2);
                ret = tmp*tmp*base;
            }else{//偶数
                double tmp = Power(base,exponent/2);
                ret = tmp*tmp;
            }
        }else{
            //奇数
            exponent = 0 - exponent;
            if(exponent%2!=0){
                double tmp = Power(base,exponent/2);
                ret = 1/(tmp*tmp*base);
            }else{//偶数
                double tmp = Power(base,exponent/2);
                ret = 1/(tmp*tmp);
            }
        }
        return ret;
  }
}

2017.5.30第二次做这道题，代码稍微简洁些：

public class Solution {
    public double Power(double base, int exponent) {
        if(exponent==0){
            return 1;
        }
        if(exponent==1){
            return base;
        }
        if(exponent<0){
            return 1/Power(base,exponent*(-1));
        }
        
        int a = exponent/2;
        int b = exponent%2;
        double c = Power(base,a);
        if(b==0){
            return c*c;
        }
        return c*c*base;
        
  }
}