347_top_K_frequent_elements.java

import java.util.SortedMap;

class Solution {
    public int[] topKFrequent(int[] nums, int k) {
        Map<Integer, Integer> numCount = new HashMap<>();
        for (int i = 0; i < nums.length; i++) {
            numCount.put(nums[i], numCount.getOrDefault(nums[i], 0) + 1);
        }
        PriorityQueue<int[]> pq = new PriorityQueue<>(new Comparator<int[]>() {
            @Override
            public int compare(int[] o1, int[] o2) {
                return o1[1] - o2[1];
            }
        });
        for (int key : numCount.keySet()) {
            int count = numCount.get(key);
            if (pq.size() == k) {
                if (pq.peek()[1] < count) {
                    pq.poll();
                    pq.offer(new int[]{key, count});
                }
            } else {
                pq.offer(new int[]{key, count});
            }
        }
        int[] ans = new int[k];
        for (int i = 0; i < k; i++) {
            ans[i] = pq.poll()[0];
        }
        return ans;
    }
}

/**
 * This is my personal record of solving Leetcode Problems. 
 * If you have any questions, please discuss them in [Issues](https://github.com/mengxinayan/leetcode/issues).
 * Copyright (C) 2020-2022  mengxinayan
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */