Given two binary strings, return their sum (also a binary string).

For example,

a = "11"

b = "1"

Return "100".

求数字字符串的二进制和。

同之前的数组代表数字，两个数组相加一样。仅仅只是进位变成了2.可能两个串的长度不一样，故逆转。从左到右加下去。最后再逆转。

	public static String addBinary(String a, String b) {

		StringBuilder ar = new StringBuilder(a).reverse();

		StringBuilder br = new StringBuilder(b).reverse();

		StringBuilder result = new StringBuilder();

		int len = Math.max(a.length(), b.length());

		int carry = 0;//进位

		for (int i = 0; i < len; i++) {

			int t1 = (i >= a.length() ? 0 : (ar.charAt(i) - '0'));

			int t2 = (i >= b.length() ? 0 : (br.charAt(i) - '0'));

			int t3 = t1 + t2 + carry;

			carry = t3 / 2;

			t3 = t3 % 2;

			result.append(t3);

		}

		if (carry != 0)

			result.append(carry);

		result.reverse();

		return result.toString();

	}