Question

I need Help PLZ ( Java Code ).

Today 14.06.2019 I have to hand in my homework.

reachability

Actually, you find flying very good, but you do not trust the whole new-fangled flying stuff and the infrastructure it has built up. As a diehard medieval metal fan you prefer to travel from A to B but rather the good old catapult. Since one can not easily take the favorite cat on vacation with it (cats do not get drafts, which is why ICEs are also eliminated), they let themselves be asked to take a plane on vacation. So you are now looking at the network spanned by airports and existing direct connections and wondering which airports are actually critical. A critical airport is an airport whose sudden disappearance would make it impossible to reach all other (remaining) airports from any (remaining) airport. For example, in the following example, the airports ICT and TXL are critical airports, but not BER:

LAS JAV BER IKT! FNJ

So you decide to write a program that will calculate the amount of critical airports for you. You can assume the following assumptions:

At the beginning, all other airports can be reached from any airport.
If a connection from airport
F1 to F2 airport will also consist of a link from F2 airport back to F1.
In the ads.set3.airports package, write a CriticalAirportFinder class and implement the following method:

/ **
* Finds whose removal causes unrealistic destinations. Thus, the
* result must be a set of airports that, if removed, cause at least one pair of
* other airports to have no path between them.
*
* @param airports set of airports.
* @return set of critical airports. Can it be empty?
* airports without a path between them in the input. Must not be
* {@code null}.
* /
public static set findCriticalAirports (Set airports) {
// TODO Implement me!
}

/************* the airport class is ***********************/

package ads.set3.airports;

import java.util.HashSet;
import java.util.Set;
import java.util.regex.Pattern;

/**
* Models an airport. For them to be identifiable, all airports have an
* IATA code and
* two airports are considered equal if their IATA codes match. Since this class
* implements {@link #equals(Object)} and {@link #hashCode()}, it can be used in
* hash-based data structures, such as {@link HashSet}.
*
*

* Each airport has a (possibly empty) set of designations that can be reached
* directly (that is, there are direct flights from this airport to all
* designation airports). If there is a direct flight from this airport to
* another airport, there will be a direct return flight as well.
*

*/
public final class Airport implements Comparable {

   /** The airport's IATA designation. */
   private final String iataDesignation;
   /** Set of airports that can be reached from this airport. */
   private final Set destinations = new HashSet<>();

   /**
   * Creates a new airport with no connected airports.
   *
   * @param iataCode the airport's non-{@code null} IATA designation.
   * @throw IllegalArgumentException if the code is invalid.
   */
   public Airport(String iataCode) {
       ensureValidIataDesignation(iataCode);
       this.iataDesignation = iataCode;
   }

   /**
   * Throws an {@link IllegalArgumentException} if the given String is not a valid
   * IATA designation.
   */
   public static void ensureValidIataDesignation(String iata) {
       if (iata == null) {
           throw new IllegalArgumentException("IATA code cannot be null.");
       }

       if (!Pattern.matches("[a-zA-Z]{3}", iata)) {
           throw new IllegalArgumentException("IATA codes must consist of three characters.");
       }
   }

   /**
   * Returns this airport's IATA designation.
   */
   public String getIataDesignation() {
       return iataDesignation;
   }

   /**
   * Returns the airport's set of destinations that can be reached directly, to be
   * modified at will.
   */
   public Set getDestinations() {
       return destinations;
   }

   @Override
   public boolean equals(Object obj) {
       if (obj instanceof Airport) {
           return ((Airport) obj).getIataDesignation().equals(this.getIataDesignation());
       } else {
           return false;
       }
   }

   @Override
   public int hashCode() {
       return getIataDesignation().hashCode();
   }

   @Override
   public int compareTo(Airport o) {
       return iataDesignation.compareTo(o.iataDesignation);
   }

}

/**********************************************************/

/******* I tried with this code but I still ve a problem with arrive methode , doesnt give me the path between the airports*****/

/********** this verboten parameter means the airports that is removed from the set *****/

Answer 1

        public static Set<Airport> findCriticalAirports(Set<Airport> airports) {

                Set<Airport> result = new HashSet<>();
                
                Iterator<Airport> iterator = airports.iterator();
                while(iterator.hasNext()) {

                        Airport currentAirport = iterator.next();
                        
                        // we will think that a airport forms a group of its own.
                        HashMap<Airport, Integer> groupParent = new HashMap<>();
                        ArrayList<Airport> otherAirports = new ArrayList<>(airports);
                        otherAirports.remove(currentAirport);
                        
                        int count = 0;

                        for(Airport a: otherAirports) {
                                groupParent.put(a, count++);
                        }

                        for(Airport s: otherAirports) {
                                for(Airport d: s.getDestinations()) {
                                        if(!d.equals(currentAirport)) {

                                                int a = groupParent.get(s);
                                                int b = groupParent.get(d);
                                                
                                                if(a != b) {
                                                        groupParent.put(s, Math.min(a, b));
                                                        groupParent.put(d, Math.min(a, b));
                                                }
                                        }
                                }
                        }
                        
                        if(new HashSet<>(groupParent.values()).size() > 1) {
                                result.add(currentAirport);
                        }
                
                }
                
                return result;
        }
                

Finds airports whose removal causes unreachable destinations. Thus, the 04 result must be a set of airports that, if one is removed, cause at least one pair of other airports to have no path between them. <terminated 05 TOS 06 STN 07 @param airports set of airports. * @return set of critical airports. Can be empty, but must not be {@code null}. 08 09 100 public static Set<Airport> findCriticalAirports (Set<Airport> airports) { 11 Set<Airport> result = new HashSet<>(); 12 13 Iterator<Airport> iterator = airports.iterator(); while(iterator.hasNext ()) { 14 15 16 Airport currentAirport = iterator.next (); 17 18 //we will think that a airport forms a group of its own. HashMap<Airport, Integer> groupParent = new HashMap<>(); Array List<Airport> otherAirports = new Array List<>(airports); otherAirports.remove(currentAirport); 19 20 21 22 23 int count = 0; 24 25 for (Airport a: otherAirports) { groupParent.put(a, count++); 26 27 28 29 for (Airport s: otherAirports) { for(Airport d: s.getDestinations()) { if (!d.equals(currentAirport)) { 30 31 32 33 34 int a groupParent.get(s); int b groupParent.get(d); 35 36 if (a !b) groupParent.put (s, Math.min (a, b)); groupParent.put(d, Math.min(a, b)); 37 38 39 40 41 42 43 44

Please upvote, as i have given the exact answer as asked in question. Still in case of any issues in code, let me know in comments. Thanks!