题目：

题解：

void reserve(char* s) {
    int len = strlen(s);
    for (int i = 0; i < len / 2; i++) {
        char t = s[i];
        s[i] = s[len - i - 1], s[len - i - 1] = t;
    }
}

char* addBinary(char* a, char* b) {
    reserve(a);
    reserve(b);

    int len_a = strlen(a), len_b = strlen(b);
    int n = fmax(len_a, len_b), carry = 0, len = 0;
    char* ans = (char*)malloc(sizeof(char) * (n + 2));
    for (int i = 0; i < n; ++i) {
        carry += i < len_a ? (a[i] == '1') : 0;
        carry += i < len_b ? (b[i] == '1') : 0;
        ans[len++] = carry % 2 + '0';
        carry /= 2;
    }

    if (carry) {
        ans[len++] = '1';
    }
    ans[len] = '\0';
    reserve(ans);

    return ans;
}