题意：实现pos(x, n)功能， 其中ｘ为double类型，n为int类型
附上代码：
1 class Solution {
2 public:
3 double pow(double x, int n) {
4 // handle several particular test cases
5 if (n == 0) return 1;
6 if (x == 1.0) return x;
7 if (x == -1.0) return n % 2 == 1 ? -1 : 1;
8 // "n" is positive or negative ?
9 bool flag = n > 0 ? true : false;
10 n = abs(n);
11 // holds the answer
12 double ans = 1.0;
13 while (n) {
14 if (n % 2) ans *= x;
15 x *= x;
16 n /= 2;
17 }
18 if (flag) return ans;
19 else return 1.0 / ans;
20 }
21 };