实现pow函数

class Solution {public:    double Power(double base, int exponent) {    double num = base,res = 1;    int exp = exponent;    if (exp == 0)        return 1;    else if (exp <0){        if (base == 0)            return -1;        exp = (-exp);    }    while (exp != 0){        if (exp % 2 != 0)            res*=num;        num *= num;        exp >>= 1;    }    return (exponent>0 ? res : (1 / res));}};

考虑base==0,exp为非正数情况