编程之美2.7节求最大公约数问题

用java写的关于求最大公约数的三种方法：

package suda.alex.chapter2;
import java.util.*;

public class Gcd {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Scanner scanner = new Scanner(System.in);
        System.out.println("please input two numbers:");
// int x = scanner.nextInt();
// int y = scanner.nextInt();
        Long x = scanner.nextLong();
        Long y = scanner.nextLong();
// System.out.println("result:"+gcd1(x, y));
// System.out.println("result:"+gcd2(x, y));
        System.out.println("result:"+gcd3(x, y));
    }

    public static int gcd1(int x, int y){
        return (y==0)?x:gcd1(y,x%y);
    }

    public static Long gcd2(Long x,Long y){
        if(x < y){
            return gcd2(y,x);
        }
        else if(y == 0){
            return x;
        }
        else{
            return gcd2(x-y,y);
        }
    }

    public static Long gcd3(Long x, Long y){
        if(x < y){
            return gcd2(y,x);
        }
        else if(y == 0){
            return x;
        }
        else{
            if(x%2 == 0){
                if(y%2 == 0)
                    return (gcd2(x>>1,y>>1)<<1);
                else
                    return gcd2(x>>1,y);

            }
            else{
                if(y%2 == 0)
                    return gcd2(x,y>>1);
                else
                    return gcd2(y,x-y);
            }
        }

    }

}