Add Binary

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

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

思路：

先将原字符串反转，对齐逐位进行相加，再把结果反转

   string addBinary(string a, string b) {
        // Note: The Solution object is instantiated only once and is reused by each test case.
        reverse(a.begin(), a.end());
        reverse(b.begin(), b.end());
        int la = a.length(),  lb = b.length(), n = min(la, lb);
        int i, carry = 0, t;
        string result = "";
        for(i = 0; i < n; i++){
            t = carry + a[i] + b[i] - '0' - '0';
            carry = t/2;
            t = t%2;
            result = result + (char)('0'+t);
        }
        if(la > lb){
            for(i = lb; i < la; i++){
                t = carry + a[i] - '0';
                carry = t/2;
                t = t%2;
                result = result + (char)('0'+t);
            }
        }
        else{
             for(i = la; i < lb; i++){
                t = carry + b[i] - '0';
                carry = t/2;
                t = t%2;
                result = result + (char)('0'+t);
            }
        }
        if(carry == 1)
            result += '1';
        reverse(result.begin(), result.end());
        return result;
    }