leetcode Add Binary

 1 class Solution {
 2 public:
 3     string addBinary(string a, string b) {
 4         int aL = a.length();
 5     int bL = b.length();
 6     int cL;
 7     if (aL > bL)
 8         cL = aL + 1;
 9     else
10         cL = bL + 1;
11     char *c = new char[cL+1];
12     int k = aL-1;
13     int j = bL - 1;
14     int flag = 0;
15     for (int i = cL - 1; i >= 1; i--)
16     {
17         if (k == -1)
18         {
19             int sum = b[j] - ‘0‘ + flag;
20             c[i] = sum%2+‘0‘;
21             flag = sum / 2;
22             j--;
23         }
24         else if (j == -1)
25         {
26             int sum = a[k] - ‘0‘ + flag;
27             c[i] = sum % 2+‘0‘;
28             flag = sum / 2;
29             k--;
30         }
31         else
32         {
33             int sum = flag + a[k]-‘0‘ + b[j]-‘0‘;
34             c[i] = sum % 2 + ‘0‘;
35             flag = sum / 2;
36             k--;
37             j--;
38         }
39     }
40     c[0] = flag + ‘0‘;
41     c[cL] = 0;
42     if (c[0] == ‘0‘)
43         return &c[1];
44     else
45         return c;
46     }
47 };