学步园

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;
    }
}