C++ solution the problem "Balanced Smileys" in the Facebook Hackecup 2013. No stacks, no recursion. Complexity is O(n).

gistfile1.cpp

bool isBalanced(const string message) {
    int paransOpen = 0;
    int maybeOpen = 0;
    int maybeClosed = 0;
    char prevChar = 0;

    string::const_iterator iter;
    for (iter = message.begin(); iter < message.end(); iter++) {
        if (*iter == '(') {
            if (prevChar == ':') {
                maybeOpen++;
            } else {
                paransOpen++;
            }
        } else if (*iter == ')') {
            if (prevChar == ':') {
                if (paransOpen > 0) { // <-- Untested fix to problem pointed out to me by Angelo Di Pilla
                    maybeClosed++;
                }
            } else {
                paransOpen--;
            }
        } else if (!isalpha(*iter) && *iter != ':' && *iter != ' ') {
            return false;
        }
        if (paransOpen + maybeOpen < 0) {
            return false;
        }
        prevChar = *iter;
    }
    if (paransOpen + maybeOpen >= 0 &&
        paransOpen - maybeClosed <= 0) {
        return true;
    } else {
        return false;
    }
}