力扣——前K个高频元素

class Solution {
    public List<Integer> topKFrequent(int[] nums, int k) {
        HashMap<Integer, Integer> map = new HashMap<>();
        for(int num : nums){
            if(!map.containsKey(num)) {
                map.put(num, 1);
            }else {
                map.put(num, map.get(num) + 1);
            }
        }
        
        PriorityQueue<Integer> queue = new PriorityQueue<>(new Comparator<Integer>() {

            @Override
            public int compare(Integer arg0, Integer arg1) {
                return map.get(arg0) - map.get(arg1);
            }
        });
        for(int key : map.keySet()) {
            if(queue.size() < k) {
                queue.add(key);
            }else if(map.get(key) > map.get(queue.peek())){
                queue.poll();
                queue.add(key);
            }
        }
        
        LinkedList<Integer> linkedList = new LinkedList<>();
        while(!queue.isEmpty()) {
            linkedList.addFirst(queue.poll());
        }
        return linkedList;
    }
}