1 public class Solution {
2 public double pow(double x, int n) {
3 // Start typing your Java solution below
4 // DO NOT write main() function
5 double result = 1.0;
6 if (n >= 0)
7 return cal(x, n);
8 else
9 {
10 n = -1 * n;
11 x = 1 / x;
12 return cal(x, n);
13 }
14 }
15 public double cal(double x, int n)
16 {
17 if (n == 0)
18 return 1.0;
19 else if (n == 1)
20 return x;
21 else if (x == 1.0)
22 return 1.0;
23 else if (x == -1.0)
24 {
25 if (n % 2 == 0)
26 return 1.0;
27 else
28 return -1.0;
29 }
30 if (n % 2 == 0)
31 {
32 double tmp = cal(x, n / 2);
33 return tmp * tmp;
34 }
35 else
36 {
37 double tmp = cal(x, (n - 1) / 2);
38 return tmp * tmp * x;
39 }
40
41 }
42 }
