Lintcode: Add Binary

C++

 class Solution {
 public:
     /**
      * @param a a number
      * @param b a number
      * @return the result
      */
     string addBinary(string& a, string& b) {
         // Write your code here
         if (a == "") {
             return b;
         }
         if (b == "") {
             return a;
         }
         string result;
         int carry = ;
         int ai, bj, sum;
         char val;
         for (int i = a.size()-, j = b.size()-; i >=  || j >= ; i--, j--) {
             ai = i >= ?a[i]-'':;
             bj = j >= ?b[j]-'':;
             sum = ai+bj+carry;
             val = sum%?'':'';
             carry = sum/;
             result.insert(result.begin(), val);
         }
         if (carry == ) {
             result.insert(result.begin(), '');
         }
         return result;
     }
 };