bool lookup(string s)
{
    // TODO
    int start = 0;
    int end = dictionary.size;

    int mid = start + end / 2;

    while (end - start > 0)
    {
        if (strcmp(s, dictionary.words[mid].letters) == 0)
        {
            return true;
        }
        if (strcmp(s, dictionary.words[mid].letters) < 0)
        {
            end = mid - 1;
        }
        if (strcmp(s, dictionary.words[mid].letters) > 0)
        {
            start = mid + 1;
        }
    }
    return false;

}