public class Main{

 static Set<String> statesNeeds = new HashSet<>();
 static String[] str = {"mt", "wa", "or", "id", "nv", "ut", "ca", "az"};

 static Map<String,Set<String>> stations = new HashMap<>();

 //初始化
 public static void Init(){
 //需要覆盖的州
 for (int i = 0; i < str.length; i++) {
 statesNeeds.add(str[i]);
 }

 //广播站
 Set<String> temp = new HashSet<>();
 temp.add("id");
 temp.add("nv");
 temp.add("ut");
 stations.put("kone", temp);

 Set<String> temp1 = new HashSet<>();
 temp1.add("wa");
 temp1.add("id");
 temp1.add("mt");
 stations.put("ktwo", temp1);

 Set<String> temp2 = new HashSet<>();
 temp2.add("or");
 temp2.add("nv");
 temp2.add("ca");
 stations.put("kthree", temp2);

 Set<String> temp3 = new HashSet<>();
 temp3.add("nv");
 temp3.add("ut");
 stations.put("kfour", temp3);

 Set<String> temp4 = new HashSet<>();
 temp4.add("ca");
 temp4.add("az");
 stations.put("kfive", temp4);

 //System.out.println(stations);
 }

 public static void main(String[] args) {

 Init();

 List<String> finalStations = new LinkedList<>();

 while (statesNeeds.size()!=0) {
 Set<String> states_covered = new HashSet<>();
 String best_stations = null;

 for (Map.Entry<String,Set<String>> entry : stations.entrySet()) {
 Set<String> states_for_station = entry.getValue();
 states_for_station.retainAll(statesNeeds); //交集 covered

 if (states_covered.size() < states_for_station.size()){
 best_stations = entry.getKey();
 states_covered = states_for_station;
 }
 }
 statesNeeds.removeAll(states_covered);
 finalStations.add(best_stations);

 }

 //结果为1.2.3.5 或者 2.3.4.5
 System.out.println(finalStations);
 }

}