LeetCode 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 len_a=a.length();
        int len_b=b.length();
        int carry=0,temp;
        string res="";
    
        int len=max(len_a,len_b);
        for(int i=0;i<len;i++){
          int p=(i<len_a)?a[len_a-1-i]-'0':0;
          int q=(i<len_b)?b[len_b-1-i]-'0':0;          
          temp=p+q+carry;
          carry=temp/2;
         res.insert(res.begin(),temp%2+'0');
        }
        
        return (carry==0)?res:"1"+res;
    }

};