JavaDeQueue.java

// https://www.hackerrank.com/challenges/java-dequeue

import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;

public class JavaDeQueue {
 private static final Scanner SCANNER = new Scanner(System.in);

 public static void main(String[] args) {

 int length = SCANNER.nextInt();
 int subArraySize = SCANNER.nextInt();
 int[] array = getArray(length);
 Map<Integer, Integer> frequencies = getElementsOfFirstSubArray(array, subArraySize);
 int maxUniqueElements = frequencies.size();

 for (int index = 0 ; index < array.length - subArraySize ; index++) {
 remove(frequencies, array[index]);
 frequencies.put(array[index + subArraySize],
 frequencies.getOrDefault(array[index + subArraySize], 0) + 1);
 maxUniqueElements = Math.max(maxUniqueElements, frequencies.size());
 }

 System.out.println(maxUniqueElements);
 }

 private static void remove(Map<Integer, Integer> frequencies, int element) {
 if (frequencies.containsKey(element)) {
 if (frequencies.get(element) <= 1) {
 frequencies.remove(element);
 } else {
 frequencies.put(element, frequencies.get(element) - 1);
 }
 }
 }

 private static int[] getArray(int length) {
 int[] array = new int[length];
 for (int index = 0 ; index < array.length ; index++) {
 array[index] = SCANNER.nextInt();
 }
 return array;
 }

 private static Map<Integer, Integer> getElementsOfFirstSubArray(int[] array, int subArraySize) {
 Map<Integer, Integer> frequencies = new HashMap<>();
 for (int index = 0 ; index < subArraySize ; index++) {
 frequencies.put(array[index], frequencies.getOrDefault(array[index], 0) + 1);
 }
 return frequencies;
 }
}