class A {

void print_state();

int *m_var;
int m_Nvar;

std::vector<std::vector<std::int> > m_doms;
std::vector<std::vector<std::int> > m_groups;
std::vector<std::string> > m_words;

int *m_cst1;
int *m_cst2;
int m_Ncst;

CwordSolver::CwordSolver(std::string words[], int num,
int c1[], int m, int c2[], int n) {

    // we are only interested, the words of length smaller than m_max_len
    // put m_max_len number of empty vectors (groups) in the group vector
    for (int i = 0; i < m_max_len; i++)
    {
        m_groups.push_back(std::vector<int>());
    }

    // go through every words and copy words of interest to m_words
    // push the index of the word to the group it belongs to (by its length)
    for (int i = 0, k = 0; i < num; i++, k++)
    {
        int len = words[i].length();
        if (len > m_max_len)
            continue;
        m_words.push_back(words[i]);
        m_groups[len].push_back(k);
    }

    // you can ignore this part: link the group to another structure
    for (int i = 0; i < m_Nvar; i++)
    {
         m_doms.push_back(m_groups[m_cst1[i]]);
    }

    ...
}

...