Add Binary

Add Binary

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

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

注意处理字符串加法的方法：

string addBinary(string a, string b)     {        string result;        const size_t n =a.size()>b.size()?a.size():b.size();                reverse(a.begin(),a.end());        reverse(b.begin(),b.end());        int carry =0;        for(size_t i=0;i<n;i++)        {            const int ai =i<a.size()? a[i] -'0':0;            const int bi =i<b.size()? b[i]-'0':0;            const int val =(ai+bi+carry)%2;            carry =(ai+bi+carry)/2;            result.insert(result.begin(),val+'0');//注意前插        }                if(carry ==1)            result.insert(result.begin(),'1');                return result;    }