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TreeSet Program Java

Write a Java program to find the numbers less than n in a tree set.

 

Java TreeSet class implements the Set interface that uses a tree for storage. It inherits AbstractSet class and implements the NavigableSet interface. The objects of the TreeSet class are stored in ascending order. And as it is a set, the elements in a treeset are unique - no duplicates.

The difference between a hashset and treeset is that, in hashset the elements are not in any order but in a treeset they are in descending order. 


Once we create a TreeSet, you can add elements to it using add() method. 

To iterate over the elements of a TreeSet, you can use an iterator interface or you can use a for each loop. But if you just want to print the elements, you can give the treeset object as a parameter to println() method.

Numbers less than n : 


To obtain elements which are less than a given key, you can use the method headSet(). This method returns a SortedSet with values which are strictly less than the given value. 

So now we are ready to write the program. 





        TreeSet<Integer> set = new TreeSet<>();    




        for(int i=0;i<5;i++){




            int num  = scanner.nextInt();




            set.add(i*i);




        }
We created a TreeSet and added n elements to it. Now if we print the set using

System.out.println(set) we get

 [0,1,4,9,16]

And 
Finally to get the subset with all elements smaller than n, we use

SortedSet subset = set.headSet(n);

Here is our complete program.

import java.util.Scanner;
import java.util.SortedSet;
import java.util.TreeSet;

public class TreeSetDemo {
    public TreeSet<Integer> createSet(int n){
        TreeSet<Integer> set = new TreeSet<>();
        Scanner scanner = new Scanner(System.in);
        for(int i=0;i<n;i++){
            int num  = scanner.nextInt();
            set.add(num);
        }
        return set;
    }
    public static void main(String args[]){
        TreeSetDemo obj = new TreeSetDemo();
        TreeSet<Integer> s1 = obj.createSet(5);
        System.out.println("Enter n:");
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        SortedSet<Integer> subset = s1.headSet(n);
        System.out.println("The elements smaller than "+n+" are"+subset);
    }
}

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