Priyanka and Toys

int cost(const vector<int>& weights) {
    if (weights.empty()) {
        return 0;
    }

    vector<bool> allWeights(10000);
    for (int w : weights) {
        allWeights[w] = true;
    }

    int count = 0;
    int i = 0;
    while (i < allWeights.size()) {
        if (allWeights[i]) {
            ++count;
            i += 5;
        } else {
            ++i;
        }
    }

    return count;
}