Class SublistGenerator

tests/utils/lists.cpp:115–180

@private

/// @private
class SublistGenerator final : public IGenerator<vector<int>> {
    
    // list of all possible (unique) elements
    vector<int> list;

    // output sublist of user-specified length
    int sublen;
    vector<int> sublist;

    // indicates which elements of list are in sublist
    vector<bool> featured;

private:

    void prepareSublist() {
        
        // choose the next combination
        int j=0;
        for (size_t i=0; i<list.size(); i++)
            if (featured[i])
                sublist[j++] = list[i];
                
        // prepare for permuting
        std::sort(sublist.begin(), sublist.end());
    }

public:

    SublistGenerator(vector<int> list, int sublen): 
        list(list),
        sublen(sublen)
    {
        // ensure sublist would not be longer than list
        DEMAND( sublen <= list.size() );

        // populate sublist with first elements
        sublist.resize(sublen);
        featured.resize(list.size());
        fill(featured.end() - sublen, featured.end(), true);

        prepareSublist();
    }

    vector<int> const& get() const override {

        // return a copy of sublist
        return sublist;
    }
    
    bool next() override {
        
        // offer next permutation of the current combination
        if (std::next_permutation(sublist.begin(), sublist.end()))
            return true;

        // else generate the next combination
        if (std::next_permutation(featured.begin(), featured.end())) {