CareerCup 1.1

1.1 Implement an algorithm to determine if a string has all unique characters. What if you cannot use additional data structure?

bool isUniqueChar(string s) {
    vector<bool> c(256, false);
    for (int i = 0; i < s.length(); i++) {
        if (c[s[i]])
            return false;
        c[s[i]] = true;
    }
    return true;
}