leetcode--Power(x,n)

Implement pow(x, n). 

divide and conquer method： the running time is O(ln n)

 

 1 public class Solution{    
 2     public double pow(double x, int n){
 3         double result = 0;
 4         long temp = n;
 5         if(temp >= 0)
 6             result = power(x, temp);
 7         else 
 8             result = 1.0 / power(x, -1 * temp);
 9             
10         return result;
11     }
12     
13     public double power(double x, long n){
14         double result = 1;
15         if( n == 0)
16             return 1;
17         if( n == 1)
18             return  x;
19 
20             //divide-and-conquer
21         result = power(x, n / 2);
22         result *= result;
23                
24                 //if n is odd       
25         if( (n % 2) == 1)
26             result *= x;
27         return result;    
28     }
29 }

 

 

 

posted @ 2014-01-29 23:38  Averill Zheng  阅读(137)  评论(0)  编辑  收藏  举报