Problem

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

The input strings are both non-empty and contains only characters 1 or 0.

Example

Input: a = "11", b = "1"
Output: "100"

Input: a = "1010", b = "1011"
Output: "10101"

Code

static int var = [](){
    std::ios::sync_with_stdio(false);
    cin.tie(NULL);
    return 0;
}();
class Solution {
public:
    string addBinary(string a, string b) {
        string res = "";
        int a_z = a.size();
        int b_z = b.size();
        if (a_z<b_z) {
            for (int i = 0; i<b_z - a_z; i++)
                a = "0" + a;
        }
        else {
            for (int i = 0; i<a_z - b_z; i++) {
                b = "0" + b;
            }
        }
        bool flag = false;
        for (int i = a.size() - 1; i >= 0; i--) {
            if (a[i] == '1' && b[i] == '1') {
                if (flag)
                    res = "1" + res;
                else
                    res = "0" + res;
                flag = true;
            }
            else if (a[i] == '0' && b[i] == '0') {
                if (flag)
                    res = "1" + res;
                else
                    res = "0" + res;
                flag = false;
            }
            else {
                if (flag)
                    res = "0" + res;
                else
                    res = "1" + res;
            }
        }
        if (flag)
            res = "1" + res;
        return res;
    }
};

Result

67. Add Binary.png