/**
 *
 * 一个7进制数字，把它转换为10进制。尽量运行快，内存占用少。不能用幂运算、不能用Math类
 * 抛砖引玉
 */
package test;
import java.util.Date;
public class NumberCase {

        
    private static int convert(int num){
        int total=0;
        int weithValue = 1;
        do{
            total = total+(weithValue)*(num%10);
            weithValue = (weithValue<<3)-weithValue;
            num = num/10;
        }while(num>0);
        return total;
    }
   
    public static int convertUseMath(int num){
        int total=0;
        for(int i=0;num>0;i++){
            //System.out.println(Math.pow(7,i));
            total = total +(int)((num%10)*Math.pow(7,i));
            num = num/10;
        }
        
        return total;
    }
   
    public static void main(String[] args) {
        int result = 0;
        long start = new Date().getTime();
        for(int i=0;i<1000000;i++){
            result = convert(1234568765);
            //result = convertUseMath(1234568765);
        }
        long end = new Date().getTime();
        System.out.println(result+">>>>>"+(end-start));
    }

}

[ 本帖最后由 西鄙人 于 2011-7-11 22:33 编辑 ]

很简单,初值n=0,然后从最高位算到最低位,如下操作
n*=7; n+={那一位的数值}