unsigned search_ok_2 (char *s, unsigned len)
{
    if (len<2)
        return len; // not found
    bool seen_o=false;
    for (unsigned i=0; i<len; i++)
    {
        char ch=s[i]; // this is single read operation
        if (ch=='o')
            seen_o=true;
        else if (seen_o && ch=='k')
            return i-1;   // found
        else
            seen_o=false; // reset
    };
    return len; // not found
};