1 public class Solution { 2     public double pow(double x, int n) { 3         if(x==0||x==1) return x; 4         if(n<0)return 1/helper(x,-1*n); 5         else return helper(x,n); 6     } 7     public double helper(double x,int n){ 8         if(n==0) return 1; 9         double res = helper(x,n/2);10         if(n%2==0) return res*res;11         else return res*res*x;12     }13 }