题意  给你两个二进制数m,n   求他们的最大公约数  用二进制表示  0<m,n<2^1000

先把二进制转换为十进制  求出最大公约数  再把结果转换为二进制  数比較大要用到大数

import java.util.*;
import java.math.*;

public class wl6_9 {

	static BigInteger two = BigInteger.valueOf(2), one = BigInteger.ONE,
			zero = BigInteger.ZERO;

	static BigInteger gcd(BigInteger a, BigInteger b) {
		while (!(a.mod(b).equals(zero))) {
			BigInteger t = a.mod(b);
			a = b;
			b = t;
		}
		return b;
	}

	static void bprint(BigInteger x) {
		if (x.equals(zero))
			return;
		bprint(x.divide(two));
		if (x.mod(two).equals(one))
			System.out.print(1);
		else
			System.out.print(0);
	}

	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		int T = in.nextInt();
		String a, b;
		for (int t = 1; t <= T; t++) {
			a = in.next();
			b = in.next();
			int la = a.length(), lb = b.length();

			BigInteger m = zero, n = zero;
			for (int i = 0; i < la; ++i) {
				m = m.multiply(two);
				if (a.charAt(i) == '1')
					m = m.add(one);
			}

			for (int i = 0; i < lb; ++i) {
				n = n.multiply(two);
				if (b.charAt(i) == '1')
					n = n.add(one);
			}
			System.out.printf("Case #%d: ", t);
			bprint(gcd(m, n));
			System.out.println();
		}
		in.close();
	}
}

Divided Land

3
10 100
100 110
10010 1100

Case #1: 10
Case #2: 10
Case #3: 110