PU Palindrome Permutation

bool canPermutePalindrome(char* s) {
    int flag[256] = {0};
    int res = 0;
    for (; *s; s++) {
        if (flag[*s]) {
            res--;
            flag[*s] = 0;
        }
        else {
            res++;
            flag[*s] = 1;
        }
    }
    return res < 2;
}