remove() and keySet() not passing

Question about the task

Under discussion

Hey, I have the same output as commented in main (also tested it a bit and everything works fine) but it's not passing. keySet() seems obvious (or not?).

@Override
public Set<K> keySet() {
    return map.keySet();
}

remove():

@Override
public V remove(Object key) {
        if( map.get(key).size() == 0 ) {
            map.remove(key);
        } else {
            V val = map.get(key).get(0);
            map.get(key).remove(0);
            return val;
        }
    return null;
}

Amigo, sometimes Java's built-in collections aren't enough. When that's the case, you can use third-party implementations, such as Google Guava or Apache Commons, or you can implement your own data structure. Today you have a unique opportunity to put your knowledge to the test and write part of your own data structure.

Our data structure is called MyMultiMap. It is a generic class, inherits HashMap, and implements the Cloneable and Serializable interfaces. Our map will be special in that its constructor will accept an int repeatCount argument, which is the number of values that a single key can store.

Implement the following methods:
1) int size() - This method must return the number of values in our collection.
2) V put(K key, V value) - This must add value using key. If key is already in the map and the number of values for key is less than repeatCount, then add value to the end of the list in the map object. If the number of values stored using key equals repeatCount, then remove the element with index zero from the map object's list and add value to the end of the list. The method must return the value of the last item added using key (but not the value we're currently adding). If key doesn't have any values yet, then return null.
3) V remove(Object key) - This method must remove a value using key. If several elements are stored using key, then the element with the index zero must be removed from the list. If an empty list is stored for key, then remove the key-value pair. The method must return the element that you removed. If the key isn't in the map, return null.
4) Set<K> keySet() - This method must return a set with all of the keys in map.
5) Collection<V> values() - This method must return an ArrayList<V> with all of the values. The order of the values in the list isn't important.
6) boolean containsKey(Object key) - This method must return true if key is in map, otherwise it must return false.
7) boolean containsValue(Object value) - this must return true if value is in map, otherwise it must return false.

See the example in the main() method.
The main() method is not tested.

Requirements:

The MyMultiMap<K, V> class must inherit HashMap<K, V> and implement the Cloneable and Serializable interfaces.
The MyMultiMap class must have a private HashMap<K, List<V>> map field.
You must implement the int size() method as outlined in the task conditions.
You must implement the boolean containsKey(Object key) method as outlined in the task conditions.
You must implement the boolean containsValue(Object value) method as outlined in the task conditions.
You must implement the V put(K key, V value) method as outlined in the task conditions.
You must implement the V remove(Object key) method as outlined in the task conditions.
You must implement the Set<K> keySet() method as outlined in the task conditions.
You must implement the Collection<V> values() method as outlined in the task conditions.

package com.codegym.task.task36.task3610; import java.util.Map; /* MyMultiMap */ public class Solution { public static void main(String[] args) { Map<Integer, Integer> map = new MyMultiMap<>(3); for (int i = 0; i < 7; i++) { map.put(i, i); } map.put(5, 56); map.put(5, 57); System.out.println(map.put(5, 58)); // Expected: 57 System.out.println(map); // Expected: {0=0, 1=1, 2=2, 3=3, 4=4, 5=56, 57, 58, 6=6} System.out.println(map.size()); // Expected: size = 9 System.out.println(map.remove(5)); // Expected: 56 System.out.println(map.remove(1)); System.out.println(map); // Expected: {0=0, 1=1, 2=2, 3=3, 4=4, 5=57, 58, 6=6} System.out.println(map.size()); // Expected: size = 8 System.out.println(map.keySet()); // Expected: [0, 1, 2, 3, 4, 5, 6] System.out.println(map.values()); // Expected: [0, 1, 2, 3, 4, 57, 58, 6] System.out.println(map.containsKey(5)); // Expected: true System.out.println(map.containsValue(57)); // Expected: true System.out.println(map.containsValue(7)); // Expected: false } }

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matemate123

Level 50 , Kraków, Poland

17 October 2023, 10:13

For others: Set requirement is good, when you repair remove() method, Set method will be green too :D

June Sung Park

Level 41 , Yangp'yong, Korea, Republic of

23 July 2020, 05:24

It seems you just need to add if (map.get(key).isEmpty()) map.remove(key); between line 53 and 54. This is to remove the key-values pair from the map, if, after deleting the value at index 0, no values remain in the list. I guess, once you fix this, the keySet() method will pass, too.

Wei Cui

Level 39 , Newark, United States

21 April 2020, 21:37

@Override
   public V remove(Object key) {
       List<V> values = map.get(key);
       if (values == null)
           return null;

       V storeValue = values.get(0);
       values.remove(0);

       if (values.size() == 0)
           map.remove(key);

       return storeValue;
   }

Kamil

Level 31 , Near Warsaw, Poland

20 April 2020, 19:58

/* Comment has been deleted */

Łukasz

Level 41 , Lodz, Poland

29 January 2020, 20:30

You need to remove "key" from the map when the list became empty, e.g: V val = map.get(key).get(0); map.get(key).remove(val); if (map.get(key).size() == 0) { map.remove(key); } return val;