Description

Submission

class Solution {
public:
    string addBinary(string a, string b) {
        if(a.size() < b.size()) swap(a, b);
        if(b == "0") return a;
        if(a == "0") return b;
        reverse(a.begin(), a.end());
        reverse(b.begin(), b.end());
        string res;
        int carry = 0;
        for(int i = 0; i < b.size(); ++i) {
            int sum = a[i] - '0' + b[i] - '0' + carry;
            carry = 0;
            if(sum < 2) res.push_back('0' + sum);
            else {
                carry = 1;
                res.push_back('0' + sum - 2);
            }
        }
        if(a.size() == b.size()) res.push_back(carry + '0');
        else {
            for(int i = b.size(); i < a.size(); ++i) {
                char sum = a[i] + carry;
                carry = 0;
                if(sum < '2') {
                    res.push_back(sum);
                } else {
                    carry = 1;
                    res.push_back(sum - 2);
                }
            }
            if(carry == 1) res.push_back('1');
        }
        reverse(res.begin(), res.end());
        return res;
    }
};