Interview Question


Country: India




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0
of 0 vote

Here is how one may define it

interfaces
-------------
Parkable
- park
- unpark




Classes
------------
Parking lot
--------
- entries
- exit(spaceid)
- entry(vehicle_type)
- full?()

Parking space
--------------------
- capacity
- size
- increment
- decrement
- location



Vehicle
-----------
- drive
- stop
- park
- unpark
-

- sarath.sp06 February 03, 2017 | Flag Reply
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0
of 0 vote

It could be defined as follows:

Composition of Parking lot and parking space by having parking spaces objects inside the parking lot class.
ParkingLot
status(full reserved)
function: find Parking. (friend of the class vehicle)

Parking space:

attributes: type (hadicapped,regular,compact)
size(small,med,large)
gate(front,back) //gate it is nearer to.

functions:
reserve();
unreserve();

Vehicle class
attributes:
type (1wheeler,car,truck)
entry gate
parked
functions: declare parking lot's findparking as a friend function.

- pc@nc March 19, 2017 | Flag Reply
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of 0 vote

enum SizeType {
    SMALL, MEDIUM, LARGE;
}

class EntryGate {
    String name;
}

class ParkingSpace {
    String id;
    SizeType size;
    EntryGate nearByGate;
}

class Vehicle {
    String number;
    SizeType size;
    EntryGate entryGate;
}

class Ticket {
    Long id;
    Date inTime;
    Vehicle vehicle;
    ParkingSpace allottedParkingSpace;

    public Ticket(Long id, Date inTime, Vehicle v, ParkingSpace p) {
        this.id = id;
        this.inTime = inTime;
        this.vehicle = v;
        this.allottedParkingSpace = p;
    }
}

public class ParkingLot {
    
    Map<SizeType, Map<EntryGate, List<ParkingSpace>>> availableParkingSpacesBySize;
    
    Map<Vehicle, Ticket> parkedVehicles;
    
    boolean isParked(Vehicle v) {
        return null != parkedVehicles.get(v);
    }
    
    private Ticket parkBySize(Vehicle vehicle, SizeType sizeType) {
        Ticket ticket = null;
        Map<EntryGate, List<ParkingSpace>> matchParking = availableParkingSpacesBySize.get(sizeType);
        if (!matchParking.isEmpty()) {
            ParkingSpace allotedParkingSpace = null;
            // prefer nearest entry gate
            EntryGate allotedEntryGate = vehicle.entryGate;
            List<ParkingSpace> availableParkingSpaces = matchParking.get(allotedEntryGate);
            
            if (!availableParkingSpaces.isEmpty()) {
                allotedParkingSpace = availableParkingSpaces.get(0);
            }
            else {
                Iterator<Map.Entry<EntryGate, List<ParkingSpace>>> itr = matchParking.entrySet().iterator();
                Map.Entry<EntryGate, List<ParkingSpace>> entry = itr.next();
                allotedEntryGate = entry.getKey();
                availableParkingSpaces = entry.getValue();
                allotedParkingSpace = availableParkingSpaces.get(0);
            }
            
            Long id = null; // generate some unique ticket id from DB
            ticket = new Ticket(id, new Date(), vehicle, allotedParkingSpace);
            
            parkedVehicles.put(vehicle, ticket);
            
            availableParkingSpaces.remove(0);
            
            if (availableParkingSpaces.isEmpty()) {
                matchParking.remove(allotedEntryGate);
            }
            
            // update vehicle ticket details in DB
        }
        
        return ticket;
    }
    
    synchronized Ticket park(Vehicle vehicle) {
        if (parkedVehicles.get(vehicle) != null) {
            // throw vehicle is already parked exception
        }
        
        Ticket ticket = null;
        
        if (!availableParkingSpacesBySize.isEmpty()) {
            ticket = parkBySize(vehicle, vehicle.size);
            if (null == ticket && vehicle.size != SizeType.LARGE) {
                if (vehicle.size == SizeType.MEDIUM) {
                    ticket = parkBySize(vehicle, SizeType.SMALL);
                }
                else if (vehicle.size == SizeType.SMALL) {
                    ticket = parkBySize(vehicle, SizeType.MEDIUM);
                    if (null == ticket) {
                        ticket = parkBySize(vehicle, SizeType.LARGE);
                    }
                }
            }
        }
        
        return ticket;
    }
    
    synchronized boolean unpark(Ticket ticket) {
        Vehicle vehicle = ticket.vehicle;
        
        Ticket t1 = parkedVehicles.get(vehicle);
        
        if (t1 == null) {
            // throw vehicle parking entry missing
        }
        
        if (!t1.equals(ticket)) {
            // throw vehicle parking ticket mismatch
        }
        
        ParkingSpace parkingSpaceToBeFreed = ticket.allottedParkingSpace;
        
        Map<EntryGate, List<ParkingSpace>> parkingSpacesBySize = availableParkingSpacesBySize.get(parkingSpaceToBeFreed.size);
        
        if (null == parkingSpacesBySize) {
            parkingSpacesBySize = new HashMap<EntryGate, List<ParkingSpace>>();
        }
        
        List<ParkingSpace> parkingSpacesByEntryGate = parkingSpacesBySize.get(parkingSpaceToBeFreed.nearByGate);
        
        if (null == parkingSpacesByEntryGate) {
            parkingSpacesByEntryGate = new ArrayList<ParkingSpace>();
        }
        
        parkingSpacesByEntryGate.add(parkingSpaceToBeFreed);
        
        parkedVehicles.remove(vehicle);
        
        return true;
    }
}

- sactiw November 28, 2017 | Flag Reply


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