67. Add Binary

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

For example,
a = "11"
b = "1"
Return "100".

字符串表示二进制数，求相加后的结果

C++（6ms）：

class Solution {
public:
    string addBinary(string a, string b) {
        string res = "" ;
        int c = 0 ;
        int i = a.size()-1 ;
        int j = b.size()-1 ;
        while(i >= 0 || j >= 0 || c == 1 ){
            c += i >= 0 ? a[i--]-'0':0 ;
            c += j >= 0 ? b[j--]-'0':0 ;
            res = char(c%2 + '0') + res ;
            c /= 2 ;
        }
        return res ;
    }
};