Leetcode-67. binary sum

Mathematical problems

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Topic details

Here are two binary strings , Returns the sum of them （ In binary ）.
Input is Non empty String and contains only numbers 1 and 0.

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Example 1：

 Input : a = "11", b = "1"
 Output : "100"

Example 2:

 Input : a = "1010", b = "1011"
 Output : "10101"

Ideas :
The question is leetcode-415. Variant of string addition , It's just that decimal has become binary , The idea is exactly the same
my 415 Detailed analysis of the problem solution :
leetcode-415. String addition

My code ：

class Solution 
{
    
public:
    string addBinary(string a, string b) 
    {
    
        string res = "";  //  Save the result 
        // Turn it around 
        reverse(a.begin(), a.end());
        reverse(b.begin(), b.end());
        int len_a = a.length(), len_b = b.length();
        if (len_a <= len_b) // Let the longer number come first 
        {
    
           swap(a, b);
           swap(len_a, len_b); 
        }
        int addbit = 0; // Carry or not 
        for (int i = 0; i < len_b; ++i) // Deal with equal length parts 
        {
    
            int cur_sum = (a[i] - '0') + (b[i] - '0') + addbit;
            res += to_string(cur_sum % 2);
            addbit = cur_sum < 2? 0 : 1;
        }
        for (int i = len_b; i < len_a; ++i)  // Handle longer parts 
        {
    
            int cur_sum = (a[i] - '0') + addbit;
            res += to_string(cur_sum % 2);
            addbit = cur_sum < 2? 0 : 1;
        }
        if (addbit)  // Process the highest bit 
        {
    
            res += "1";
        }
        reverse(res.begin(), res.end()); // Turn back 
        return res;

    }
};