4.Add Binary

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

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

Example 2:
Input: a = "1010", b = "1011"
Output: "10101"

Solution:

class Solution
{
public:
    string addBinary(string a, string b)
    {

        int l1 = a.length() - 1;
        int l2 = b.length() - 1;
        string s = "";
        int res, carry = 48;
        int x,y,sum;
        while (l1 >= 0 && l2 >= 0)
        {
             x = int(a[l1]);
             y = int(b[l2]);
            res = (x + y + carry) % 2;
            carry = (x + y + carry - 48)/2; 
            cout<<carry<<" ";
            if (res == 0)
            {
                s = '0' + s;
            }
            else
            {
                s = '1' + s;
            }

            l1--;
            l2--;
        }

        while (l1 >= 0)
        {
            x = int(a[l1]);
            res = (x + carry) % 2;
            carry = (x + carry) / 2;
            if (res == 0)
            {
                s = '0' + s;
            }
            else
            {
                s = '1' + s;
            }
            l1--;
        }
        
        while (l2 >= 0)
        {
             x = int(b[l2]);
            res = (x + carry) % 2;
            carry = (x + carry) / 2;
 
            if (res == 0)
            {
                s = '0' + s;
            }
            else
            {
                s = '1' + s;
            }
            l2--;
        }

        if (carry != 48)
        {
            s='1'+s;
        }

        return s;
    }
};

Time Complexity : O(n+m)