Pow(x, n)

public class Solution {
    public double pow(double x, int n) {
        return n >= 0 ? helper(x,n) : 1/helper(x,-1*n);
    }
    public double helper(double x, int n)
    {
        if(n == 0) return 1;
        if(n == 1) return x;
        double left = helper(x, n/2);
        return n%2==0? left*left : left*left*x;
    }
}

class Solution {
public  double pow(double x, int n) {
        double res=1;
         if(n<0){
            x=1/x;
            n=-n;
        }
        while(n>0){
            if(n&1==1){
                res=res*x;
            }
            x*=x;
            n=n>>1;
        }
        return res;
    }
};