50. Pow(x, n) (INT; Divide-and-Conquer)

Implement pow(x, n).

思路：二分法，将每次相乘，转化成平方。

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

        double result = myPow(x, n/);
        result*= result;
        if(n%==) result = x * result;
        else if(n%==-) result = (/x) * result; //negative number
        return result;
    }
};