Given an integer array nums and an integer k, return the k most frequent elements. You may return the answer in any order.

Example 1:

Input: nums = [1,1,1,2,2,3], k = 2 Output: [1,2]

Example 2:

Input: nums = [1], k = 1 Output: [1]

Constraints:

1 <= nums.length <= 105
-104 <= nums[i] <= 104
k is in the range [1, the number of unique elements in the array].
It is guaranteed that the answer is unique.

Follow up: Your algorithm's time complexity must be better than O(n log n), where n is the array's size.

SOLUTION:

class Solution {
    public int[] topKFrequent(int[] nums, int k) {
        int[] arr = new int[k];
        HashMap<Integer, Integer> map = new HashMap<>();
        for (int num : nums) map.put(num, map.getOrDefault(num, 0) + 1);
        PriorityQueue<Map.Entry<Integer, Integer>> pq = new PriorityQueue<>(
                (a, b) ->
            a.getValue() - b.getValue()
        );
        for (Map.Entry<Integer, Integer> it : map.entrySet()) {
            pq.add(it);
            if (pq.size() > k) pq.poll();
        }
        int i = k;
        while (!pq.isEmpty()) {
            arr[--i] = pq.poll().getKey();
        }
        return arr;
    }
    }