67. Add Binary，67addbinary

67. Add Binary，67addbinary

Given two binary strings, return their sum (also a binary string).

For example,
a = "11"
b = "1"
Return "100".

題目：求2個二進制字符串的和，結果也要二進制字符串輸出。

 1 char* addBinary(char* a, char* b) {
 2     int i = strlen(a)-1;
 3     int j = strlen(b)-1;
 4     int c = 0;
 5     char temp;
 6     char *p = (char*)malloc(i > j ? i+3 :j+3);         //分配字符串空間
 7     char *s = p;
 8     while(i >= 0 || j >= 0 || c == 1)
 9     {
10         c += i >= 0 ? a[i--] - 48 : 0;                  //字符串每一位相加
11         c += j >= 0 ? b[j--] - 48 : 0;
12         *s++ = c % 2 + 48;                              
13         c = c/2;                                        //根據c的值每次要進位
14     }
15     *s = '\0';
16     i = 0;
17     j = strlen(p)-1;
18     while(i < j)                                      //反轉字符串
19     {
20         temp = p[j];
21         p[j] = p[i];
22         p[i] = temp;
23         i++;
24         j--;
25     }
26     return p;
27 }