LEETCODE: Pow(x, n)

Implement pow(x, n).

用递归吧，虽然我尝试了用非递归，但是没有成功。

class Solution {
public:
    double powinternal(double x, int n) {
        if(n == 0) return 1;
        
        double half = powinternal(x, n / 2);
        
        if(n % 2 == 0) {
            return half * half;
        }
        else {
            return half * half * x;
        }
        
    }
    double pow(double x, int n) {
        if(n > 0)
            return powinternal(x, n);
        else
            return 1.0 / powinternal(x, -n);
    }
};