LeetCode : Add Binary

"11"

"1"

"100"

class Solution {
public:
string addBinary(string a, string b) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
int i = a.size();
int j = b.size();
if(i == 0) return b;
if(j == 0) return a;
int carry = 0;
string res;
--j;
--i;
while(i >= 0 && j >= 0){
int temp = a[i] - '0' + b[j] - '0' + carry;
carry = temp / 2;
temp %= 2;
res += (char)(temp + '0');
--i;
--j;
}
while(i >= 0){
int temp = a[i] - '0' + carry;
carry = temp / 2;
temp %= 2;
res += (char)(temp + '0');
--i;
}
while(j >= 0){
int temp = b[j] - '0' + carry;
carry = temp / 2;
temp %= 2;
res += (char)(temp + '0');
--j;
}
if(carry){
res += "1";
}
reverse(res.begin(), res.end());
return res;
}
};