1 //题目：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。 2 //分情况考虑： 3 //第一种情况：底数是0，且指数是负数； 4 //第二种情况：指数小于0； 5 class Solution  6 { 7 public: 8     bool g_InvalidInput = false; 9     double Power(double base, int exponent) 10     {11         //第一种情况：12         if (Equal(base, 0.0) && exponent < 0)13         {14             g_InvalidInput = true;15             return 0.0;16         }17         //第二种情况：考虑指数问题,指数小于0，就要取绝对值18         unsigned int absExponent = (unsigned int ) exponent;19         if (exponent < 0)20         {21             absExponent = (unsigned int)(-exponent);22         }23         double result = PowerWithExponent(base, absExponent);24         if(exponent < 0)25         {26             result = 1.0 /result;27         }28         return result;29     }30 private:31     bool Equal(double num1, double num2)32     {33         if(num1 - num2 > -0.000001 && num1-num2 <0.000001)34         {35             return true;36         }37         return false;38     }39     double PowerWithExponent(double base, unsigned int num)40     {41         if (num == 0)42         {43             return 1;44         }45         if (num == 1)46         {47             return base;48         }49         //***重点理解***由于要递归，故要定义返回值result，终止条件为num == 150         double result = PowerWithExponent(base, num>>1);51         result *= result;52         if (num & 0x1 == 1)53         {54             result *= base;55         }56         return result;57     }58 };