fill-cells-initial.cpp

bool fillCells() {
    for(auto cell : this->cells()) {
     
        // get first cell and tail
        auto cell = remainingCells.front();
        remainingCells.pop_front();

        set<int> neighborValues = {};

        for(auto &neighbor : cell->neighbors) {
            auto value = this->at(neighbor)->value;
            neighborValues.insert(value);
        }

        vector<int> options;
        set_difference(VALID_VALUES.begin(), VALID_VALUES.end(),
                        neighborValues.begin(), neighborValues.end(),
                        inserter(options, options.begin())
        );
        random_shuffle(options.begin(), options.end());
        cell->value = options[0];
    }
}