[LeetCode] Add Binary

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

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

class Solution 
{
    public:   
        string addBinary(string a, string b)
        {   
            string c;
            int carry =  0;  
            int tmp = 0;
            int size = max(a.size(), b.size());
    
            //逆序，更好处理
            reverse(a.begin(), a.end());
            reverse(b.begin(), b.end());


            for(int i = 0; i < size ; i++)
            {   
                int ta = 0;
                int tb = 0;
                if(i < a.size()) //越界处理
                    ta = a[i] - '0';//处理字符串
                if(i < b.size()) //越界处理
                    tb = b[i] - '0';//处理字符串

                tmp =  ta + tb + carry;
                c.insert(c.begin(), tmp % 2 + '0');
                carry  =  tmp / 2;
            }   

            if(carry != 0)
                c.insert(c.begin() ,'1');
            return c;
        }   
} ;