67. Add Binary

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

The input strings are both non-empty and contains only characters 1 or 0.

Example 1:

Input: a = "11", b = "1"
Output: "100"
Example 2:

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

class Solution {
public:
    string addBinary(string a, string b) {
         
       int length=max(a.size(),b.size());
        
        string temp_a;
        string temp_b;
        string temp_c;
        int arr=0;

        for(int i=a.size()-1;i>=0;i--)
            if(a[i]=='1') temp_a=temp_a+"1";
            else temp_a=temp_a+"0";
           
        for(int j=b.size()-1;j>=0;j--)
              if(b[j]=='1') temp_b=temp_b+"1";
            else temp_b=temp_b+"0";
        
         
        for(int i=a.size();i<length;i++)
            temp_a=temp_a+"0";
        for(int j=b.size();j<length;j++)
            temp_b=temp_b+"0";
 
        for(int i=0;i<length;i++)
        {
            int k=temp_a[i]-'0'+temp_b[i]-'0'+arr;
             if(k==3) {temp_c=temp_c+"1";arr=1;}
           else if(k==2) {temp_c=temp_c+"0";arr=1;}
            else if(k==1) {temp_c=temp_c+"1";arr=0;}
            else  {temp_c=temp_c+"0";arr=0;}
     
            
        }
       
        if(arr==1) temp_c=temp_c+"1";
        string result;
        
   for(int i=temp_c.size()-1;i>=0;i--)
        if(temp_c[i]=='1') result=result+"1"; 
        else result=result+"0";
        
        return result;        

    }
};