50. Pow(x, n)

Implement pow(x,n).

思路：递归

public class Solution {
    public double myPow(double x, int n) {
        if(n<0){
            return 1/power(x,-n);
        } else{
            return power(x,n);
        }
    }

    public double power(double x, int n){
        if(n==0) return 1;
        double v = power(x,n/2);

        if (n%2==0){
            return v*v;
        }else{
            return v*v*x;
        }
    }
}