leetcode 67. Add Binary

 1 string addBinary(string a, string b) 
 2     {
 3         if (a.size() == 0)
 4             return b;
 5         if (b.size() == 0)
 6             return a;
 7         
 8         reverse(a.begin(), a.end());
 9         reverse(b.begin(), b.end());
10         int carry = 0, i = 0;
11         string c = "";
12         while (i < a.size() || i < b.size())
13         {
14             int x = (i < a.size()) ? (a[i] - ‘0‘) : 0;
15             int y = (i < b.size()) ? (b[i] - ‘0‘) : 0;
16             if ((x + y + carry) & 1)
17                 c += "1";
18             else
19                 c += "0";
20             carry = (x + y + carry) >> 1;
21             i++;
22         }
23         if (carry > 0)
24             c += "1";
25         reverse(c.begin(), c.end());
26         
27         return c;
28     }