67. Add Binary

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

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

题目：求2个二进制字符串的和，结果也要二进制字符串输出。

char* addBinary(char* a, char* b) {
    int i = strlen(a)-1;
    int j = strlen(b)-1;
    int c = 0;
    char temp;
    char *p = (char*)malloc(i > j ? i+3 :j+3);         //分配字符串空间
    char *s = p;
    while(i >= 0 || j >= 0 || c == 1)
    {
        c += i >= 0 ? a[i--] - 48 : 0;                  //字符串每一位相加
        c += j >= 0 ? b[j--] - 48 : 0;
        *s++ = c % 2 + 48;                              
        c = c/2;                                        //根据c的值每次要进位
    }
    *s = '';
    i = 0;
    j = strlen(p)-1;
    while(i < j)                                      //反转字符串
    {
        temp = p[j];
        p[j] = p[i];
        p[i] = temp;
        i++;
        j--;
    }
    return p;
}