1 class Solution {
 2 public:
 3     string addBinary(string a, string b) {
 4 
 5 
 6         if( a.length() > b.length() )
 7         {
 8             string tmp = a;
 9             a = b;
10             b = tmp;
11         }
12         
13         string zero = "0";
14 
15         while( a.length() != b.length() )
16         {
17             a = zero + a;
18         }
19 
20 
21         int len = b.length();
22         int carry = 0;
23 
24         string res = "";
25         for( int i = 1 ; i <= len ; i++ )
26         {
27             int cur = 0;
28             cur = a[len-i] - ‘0‘ + b[len-i] - ‘0‘ + carry;
29             if( cur > 1 )
30             {
31                 cur -= 2;
32                 carry = 1;
33             }
34             else
35             {
36                 carry = 0;
37             }
38             char tmp = cur + ‘0‘;
39             res = tmp + res; 
40         }
41 
42         if( carry != 0 )
43         {
44             char tmp = carry + ‘0‘;
45             res = tmp + res;
46         }
47 
48         return res;
49     }
50 };