Leetcode 50 Pow(x, n)

Implement pow(x, n).
Solution 1: key is to deal with all corner case and use temp to store mid result.

 public class Solution {  
   public double myPow(double x, int n) {  
     if (x==1) return 1;  
     if (x==-1) return (n%2==1)?-1:1;  
     if (x==0) return 0;  
     if (n==0) return 1;  
     if (n<0) return 1/myPow(x,-n);  
     if (n==1) return x;  
     double mid=myPow(x,n/2);  
     double res=mid*mid; //important here, make sure mid is only cal one time  
     if (n%2==1) res*=x;  
     return res;  
   }  
 }