Java代碼之"求a的N次方"

二分法：

 
          package com.test; 
          
 
          
 
          public  
          class Power { 
          
 
          
     
          public  
          static  
          void main(String[] args) { 
          
        System.out.print("Hello, \r\n"); 
          
         
          
        System.out.print(power2(3, 2) + "\r\n"); 
          
        System.out.print(power(3, 2) + "\r\n"); 
          
         
          
        System.out.print(power2(3, 3) + "\r\n"); 
          
        System.out.print(power(3, 3) + "\r\n"); 
          
         
          
        System.out.print(power2(3, 32) + "\r\n"); 
          
        System.out.print(power(3, 32) + "\r\n"); 
          
    } 
          
 
          
     
          static  
          long power( 
          long a,  
          int n) { 
          
         
          long r = 1; 
          
         
          int t = 0; 
          
         
          while (n >= 1) { 
          
             
          if ((n & 1) == 1) { 
          
                r *= a; 
          
                t++; 
          
            } 
          
            a *= a; 
          
            t++; 
          
            n = n >> 1; 
          
        } 
          
        System.out.print(t + "times \r\n"); 
          
         
          return r; 
          
    } 
          
     
          
     
          static  
          long power2( 
          long a,  
          int n) { 
          
         
          long r = 1; 
          
         
          while (n-- >= 1) { 
          
            r =r *  a; 
          
        } 
          
         
          return r; 
          
    } 
          
}