LeetCode 67. Add Binary

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

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

这个题目只要注意各种情况你就成功了一大半，特别要注意的是对进位赋值后可能产生的变化，以及最后一位进位为1时，

我们要把这个1插进来。同时注意字符串的低位是我们数值的高位

class Solution {
public:
    string addBinary(string a, string b) {
        reverse(begin(a), end(a));
        reverse(begin(b), end(b));
        string result;
        char num = '';
        int i = ;
        for (;i < a.size() && i < b.size();++i)
        {
            if (a[i] == ''&&b[i] == ''&&num == '')
            {
                result.insert(begin(result), '');
            }
            if (a[i] == ''&&b[i] == ''&&num == '')
            {
                result.insert(begin(result), '');
            }
            if ((a[i] == ''&&b[i] == ''&&num == '') || (a[i] == ''&&b[i] == ''&&num == '') ||
                (a[i] == ''&&b[i] == ''&&num == ''))
            {
                result.insert(begin(result), '');
                num = '';
            }
            if (a[i] == ''&&b[i] == ''&&num == '' || a[i] == ''&&b[i] == ''&&num == '' ||
                a[i] == ''&&b[i] == ''&&num == '')
            {
                result.insert(begin(result), '');
                num = '';
            }
        }
        if (i == a.size())
        {
            for (;i < b.size();++i)
            {
                if (b[i] == ''&&num == '')
                    result.insert(begin(result), '');
                if (b[i] == ''&&num == '' || b[i] == ''&&num == '')
                {
                    result.insert(begin(result), '');
                    num = '';
                }
                if (b[i] == ''&&num == '')
                    result.insert(begin(result), '');
            }
        }
        else
        {
            for (;i < a.size();++i)
            {
                if (a[i] == ''&&num == '')
                    result.insert(begin(result), '');
                if (a[i] == ''&&num == '')
                    result.insert(begin(result), '');
                if (a[i] == ''&&num == '' || a[i] == ''&&num == '')
                {
                    result.insert(begin(result), '');
                    num = '';
                }

            }
        }
        if (num == '')result.insert(begin(result), '');
        return result;
    }
};