题目：本质是求两个数的最大公约数，java大数真好用 ^_^。

import java.math.BigInteger;
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        
    	BigInteger TWO = BigInteger.valueOf(2);
        Scanner t = new Scanner(System.in);
        int cas = t.nextInt();
         for(int ca=1;ca<=cas;ca++)
         {
             String a=t.next();
             String b=t.next();
             BigInteger A = cal(a);
             BigInteger B = cal(b);
             BigInteger C = A.gcd(B);
             BigInteger []D = new BigInteger[1010];
             int i=0;
             while(!C.equals(BigInteger.ZERO))
             {
            	 D[i++] = C.mod(TWO);
            	 C = C.divide(TWO);
             }
             System.out.print("Case #"+ca+": " );
             for(i--;i>=0;i--)
             System.out.print(D[i]);
             System.out.println();
         }
    }
    
    public static BigInteger cal(String s)
    {
    	char b = '1';
    	BigInteger t = BigInteger.valueOf(0);
    	BigInteger k = BigInteger.valueOf(1);
    	BigInteger TWO = BigInteger.valueOf(2);
    	for(int i=s.length()-1;i>=0;i--)
    	{
    		if(s.charAt(i)==b)
    		{
    			t=t.add(k);
    		}
    		k=k.multiply(TWO);
    	}
    	//System.out.println(t);
    	return t;
    }
}

hdu 5050 Divided Land