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HashSets

Problem Description

The Set interface of the Java Collections framework provides the features of the mathematical set in Java. It extends the Collection interface.

Unlike the List interface, sets cannot contain duplicate elements.

Since Set is an interface, we cannot create objects from it.

In order to use functionalities of the Set interface, we can use these classes:

• HashSet
• EnumSet
• TreeSet

In Java, we must import java.util.Set package in order to use Set.

```// Set implementation using HashSet
Set<string> animals = new HashSet<>()
```

Here, we have created a Set called animals. We have used the HashSet class to implement the Set interface.

Methods of Set:

The Set interface includes all the methods of the Collection interface. It’s because Collection is a super interface of Set.

Some of the commonly used methods of the Collection interface that’s also available in the Set interface are:

• addAll() - adds all the elements of the specified collection to the set
• remove() - removes the specified element from the set
• clear() - removes all the elements from the set
• size() - returns the length (number of elements) of the set
• toArray() - returns an array containing all the elements of the set
• contains() - returns true if the set contains the specified element

To learn about more methods of the Setinterface, visit Java Set (official Java documentation).

The LinkedHashSet is an ordered version of HashSet that maintains a doubly-linked List across all elements. When the iteration order is needed to be maintained this class is used. When iterating through a HashSet the order is unpredictable, while a LinkedHashSet lets us iterate through the elements in the order in which they were inserted. When cycling through LinkedHashSet using an iterator, the elements will be returned in the order in which they were inserted.

Given an integer array A you need to find the total number of unique elements in that array A.

Problem Constraints

1 <= |A| <= 105

1 <= A[i] <= 109

Input Format

The first-line contain a single integer N denoting the size of the array A.

Next N lines each contain a single integer denoting the array A elements.

Output Format

Print a single integer denoting the total number of unique elements in that array A.

Example Input

Input 1;

``` 5
1
1
3
1
2
```

Example Output

Output 1;

``` 3
```

Example Explanation

Explanation 1;

``` Unique elements are : [1, 2, 3]
```

Hints
• Complete Solution

Discussion

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