[LeetCode] Add Binary

问题：

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

For example,
a = "11"
b = "1"
Return "100".

分析：

简单的一道题，功夫在于代码写得简洁漂亮。

代码：

class Solution {
public:
	string addBinary(string a, string b) {
		int index = max(a.length(), b.length());
		string result (index + 1, '0');
		int carry = 0;
		int i = a.length() - 1;
		int j = b.length() - 1;
		while (i>= 0 || j >= 0 || carry > 0) {
			int a_num = (i >= 0? a[i --] - '0' : 0);
			int b_num = (j >= 0? b[j --] - '0' : 0);
			result[index --] = ((a_num + b_num + carry) % 2) + '0';
			carry = ((a_num + b_num + carry) > 1);
		}
		if (result[0] == '0')
			return result.substr(1);
		return result;
	}
};