public ArrayList<Thief> ranking(){
        ArrayList<Thief> winners = new ArrayList<>();
        population.thieves.sort(Thief::compareTo);
        for(int i = 0; i<POPULATION_SIZE; i++){
            for(int j = 0; j<20; j++){
                winners.add(population.thieves.get(j));
            }
        }
        return winners;
    }