题目：

题解：

class Solution {
public:
    string addBinary(string a, string b) {
        string ans;
        reverse(a.begin(), a.end());
        reverse(b.begin(), b.end());

        int n = max(a.size(), b.size()), carry = 0;
        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');
        }
        reverse(ans.begin(), ans.end());

        return ans;
    }
};