實現函式double Power(double base, int exponent)，求base的exponent次方。不得使用庫函式，同時不需要考慮大數問題。

示例 1:

輸入: 2.00000, 10
輸出: 1024.00000
示例2:

輸入: 2.10000, 3
輸出: 9.26100
示例3:

輸入: 2.00000, -2
輸出: 0.25000
解釋: 2-2 = 1/22 = 1/4 = 0.25

說明:

-100.0 <x< 100.0
n是 32 位有符號整數，其數值範圍是[−231,231− 1] 。

code1：迭代

class Solution {
public:
    double myPow(double
 
 x, int n) {
        if(n == 1 || n == 0) {
            return n == 1 ? x : 1;
        }

        int sign = 1;
        long num = n;
        if (num < 0) {
            sign = -1;
            num = -num;
        }

        double res = 1;
        while (num) {
            if (num & 1) {
                res 
 
*= x;
            }
            x *= x;
            num >>= 1;
        }

        return sign == 1 ? res : 1 / res;
    }
};

code2：遞迴

class Solution {
private:
    double myPowCore(double x, int n) {
        if (n == 0) {
            return 1;
        }

        double res = myPowCore(x, n/2);
        
 
if(n & 1) {
            return res * res * x;
        }
        else {
            return res * res;
        }
    }
public:
    double myPow(double x, int n) {
        if(n == 1 || n == 0) {
            return n == 1 ? x : 1;
        }

        if(n > 0){
            return myPowCore(x, n);
        }
        return myPowCore(1/x, n);
    }
};