How can I make a function work for both string and wstring?

If I want a function like the following to work on basic_string and basic_string what should I do? Note that it has to change wchar_t in the unordered map.

bool isUnique(wstring s)
{
    if (s.size() <= 1)
    {
        return true;
    }
    unordered_map<wchar_t, bool> charSeen;
    for (int i = 0; i < s.size(); i++)
    {
        if (!charSeen[s[i]])
        {
            charSeen[s[i]] = true;
        }
        else
        {
            return false;
        }
    }
    return true;
}
int main(int argc, char *argv[]) {
    cout << isUnique(L"فعه");
    return 0;
}