###### tags: `leetcode`
# Question 67. Add Binary
### Description:
Given two binary strings a and b, return their sum as a binary string.
### Solution:

shift and bit calculation

### AC code

class Solution {
public:
    string addBinary(string a, string b) {
        string ret = "";
        int carry = 0;
        for(int i = a.size()-1, j = b.size()-1; i >=0 || j >=0; j--, i--){
            int m = (i >=0 && a[i] == '1');
            int n = (j >=0 && b[j] == '1');
            ret = to_string((m+n+carry) & 0x1 )+ret;
            carry = (m+n+carry) >> 1;
        }
        return carry? '1'+ret:ret;
    }
};