给你两个二进制字符串，求和

#include <string>

class Solution
{
public:
	std::string addBinary(std::string a, std::string b)
	{
		std::string ans;
		std::reverse(a.begin(), a.end());
		std::reverse(b.begin(), b.end());
		int n = std::max(a.size(), b.size()), carry = 0; //进位记录

		for (size_t i = 0; i < n; ++i)
		{
			carry += i < a.size() ? (a.at(i) == '1') : 0;
			carry += i < b.size() ? (b.at(i) == '1') : 0;
			ans.push_back((carry % 2) ? '1' : '0');
			carry /= 2;
		}
		if (carry) ans.push_back(1);
		std::reverse(ans.begin(), ans.end());
		return ans;
	}
};