Java Dequeue | HackerRank Solution

Hello coders, today we are going to solve Java Dequeue HackerRank Solution.

Java Dequeue


In computer science, a double-ended queue (dequeue, often abbreviated to deque, pronounced deck) is an abstract data type that generalizes a queue, for which elements can be added to or removed from either the front (head) or back (tail).

Deque interfaces can be implemented using various types of collections such as LinkedList or ArrayDeque classes. For example, deque can be declared as:

 Deque deque = new LinkedList<>();
 Deque deque = new ArrayDeque<>();

In this problem, you are given N integers. You need to find the maximum number of unique integers among all the possible contiguous subarrays of size M.
Note: Time limit is 3 second for this problem.

Input Format

The first line of input contains two integers N and M: representing the total number of integers and the size of the subarray, respectively. The next line contains N space separated integers.


  • 1 <= N <= 100000
  • 1 <= M <= 100000
  • M <= N
  • The numbers in the array will range between [10000000].

Output Format

Print the maximum number of unique integers among all possible contiguous subarrays of size M.

Sample Input

 6 3
 5 3 5 2 3 2

Sample Output



In the sample testcase, there are 4 subarrays of contiguous numbers.

  • s1 = <5,3,5> – Has 2 unique numbers.
  • s2 = <3,5,2> – Has 3 unique numbers.
  • s3 = <5,2,3> – Has 3 unique numbers.
  • s4 = <2,3,2> – Has 2 unique numbers.

In these subarrays, there are 2,3,3,2 unique numbers, respectively. The maximum amount of unique numbers among all possible contiguous subarrays is 3.

Solution – Java Dequeue

import java.util.*;

public class test {
    public static void main(String[] args) {
        Scanner in = new Scanner(;
        Deque<Integer> deque = new ArrayDeque<>();
        HashSet<Integer> set = new HashSet<>();
        int n = in.nextInt();
        int m = in.nextInt();
        int max = Integer.MIN_VALUE;

        for (int i = 0; i < n; i++) {
            int input = in.nextInt();
            if (deque.size() == m) {
                if (set.size() > max) max = set.size();
                int first = deque.remove();
                if (!deque.contains(first)) set.remove(first);

Disclaimer: The above Problem ( Java Dequeue ) is generated by Hacker Rank but the Solution is Provided by CodingBroz. This tutorial is only for Educational and Learning Purpose.

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