Pow(x, n)

 1 class Solution {
 2 public:
 3     double pow(double x, int n) {
 4         if(x < 0) return n % 2 == 0 ? pow(-x, n) : -pow(-x, n);
 5         if(x == 0 || x == 1) return x;
 6         if(n == 0) return 1.0;
 7         if(n < 0) return 1.0/pow(x, -n);
 8         
 9         double half = pow(x, n/2);
10         if(n % 2 == 0) return half * half;
11         else return x * half * half;
12     }
13 };