Top K Elements

Given a non-empty array of integers, return the k most frequent elements.

Example 1:

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

Example 2:

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

Code

class Solution {
    public List<Integer> topKFrequent(int[] nums, 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>> maxHeap = 
            new PriorityQueue<>((a, b) -> (b.getValue() - a.getValue()));

        for(Map.Entry<Integer, Integer> entry : map.entrySet()){
            maxHeap.add(entry);
        }

        List<Integer> res = new ArrayList<>();
        while(res.size() < k){
            Map.Entry<Integer, Integer> entry = maxHeap.poll();
            res.add(entry.getKey());
        }
        return res;
    }
}