KLargestElements.java

// K Largest Elements
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// You are given with an integer k and an array of integers that contain numbers
// in random order. Write a program to find k largest numbers from given array.
// You need to save them in an array and return it.
// Time complexity should be O(nlogk) and space complexity should be not more
// than O(k).
// Order of elements in the output is not important.
// Input Format :
// Line 1 : Size of array (n)
// Line 2 : Array elements (separated by space)
// Line 3 : Integer k
// Output Format :
// k largest elements
// Sample Input :
// 13
// 2 12 9 16 10 5 3 20 25 11 1 8 6
// 4
// Sample Output :
// 12
// 16
// 20
// 25

import java.util.ArrayList;
import java.util.Collections;
import java.util.PriorityQueue;

public class Solution {

    public static ArrayList<Integer> kLargest(int input[], int k) {
        /*
         * Your class should be named Solution
         * Don't write main().
         * Don't read input, it is passed as function argument.
         * Return output and don't print it.
         * Taking input and printing output is handled automatically.
         */
        PriorityQueue<Integer> pq = new PriorityQueue<>(Collections.reverseOrder());
        for (int i : input) {
            pq.add(i);
        }

        ArrayList<Integer> arr = new ArrayList<>();
        while (k > 0) {
            arr.add(pq.poll());
            k--;
        }
        return arr;

    }
}