Class TopKElements

patterns/java/TopKElements.java:6–151

import java.util.*;

public class TopKElements {

    /*
    * ********** K Largest Elements **********
    */
    
    public int[] kLargestElementsSortingAppraoch(int[] nums, int k) {
        // Step 1: Sort the array in descending order
        Integer[] numsArray = Arrays.stream(nums).boxed().toArray(Integer[]::new);
        Arrays.sort(numsArray, Collections.reverseOrder());

        // Step 2: Extract the first K elements
        int[] result = new int[k];
        for (int i = 0; i < k; i++) {
            result[i] = numsArray[i];
        }
        return result;
    }

    public int[] kLargestElementsMaxHeapAppraoch(int[] nums, int k) {
        // Max heap
        PriorityQueue<Integer> maxHeap = new PriorityQueue<>(Collections.reverseOrder());

        // Add all numbers to the max heap
        for (int num : nums) {
            maxHeap.add(num);
        }

        // Extract the top K largest elements
        int[] result = new int[k];
        for (int i = 0; i < k; i++) {
            result[i] = maxHeap.poll();  // Extracts the largest element
        }
        return result;
    }

    public int[] kLargestElementsMinHeapAppraoch(int[] nums, int k) {
        // Min heap
        PriorityQueue<Integer> minHeap = new PriorityQueue<>();

        // Add first K elements into the min heap
        for(int i = 0; i < k; i++) {
            minHeap.add(nums[i]);
        }

        // Process the remaining elements
        for (int i = k; i < nums.length; i++) {
            minHeap.add(nums[i]);
            if (minHeap.size() > k) {
                minHeap.poll();
            }
        }

        // Extract the top K largest elements from the min heap
        int[] result = new int[k];
        for (int i = 0; i < k; i++) {
            result[i] = minHeap.poll();
        }