public String multiply(String a, String b) {
		// Start typing your Java solution below
		// DO NOT write main() function
		if ("0".equals(b) || "0".equals(a)) // 先排除，不然后面排除更麻烦
			return "0";
		int m = a.length();
		int n = b.length();
		if (m < n) {
			String c = a;
			int p = m;
			a = b;
			b = c;
			m = n;
			n = p;
		}
		int cnt = 0;
		String res = "0";
		while (n > 0) {
			String tmpRes = subTask(a, b.substring(Math.max(0, n - 4), n));
			n -= 4;
			for (int i = 0; i < cnt; i++)
				tmpRes += "0000";
			cnt++;
			res = sumTask(tmpRes, res);
		}
		return res;
	}