LeetCode 347 Top K Frequent Elements

方法1: 声明新的类 ＋ hashmap ＋ priority queue

 

class Solution {
    public List<Integer> topKFrequent(int[] array, int k) {
        Queue<Result> queue = new PriorityQueue<Result>(newComparator);
        Map<Integer, Integer> map = new HashMap<>();
        for (int i = 0; i < array.length; i++) {
            if (map.containsKey(array[i])) {
                map.put(array[i], map.get(array[i]) + 1);
            } else {
                map.put(array[i], 1);
            }
        }
        for(int i : map.keySet()) {
            queue.offer(new Result(i, map.get(i)));
        }

        List<Integer> res = new ArrayList<>();
        for (int i = 0; i < k; i++) {
            res.add(queue.poll().val);
        }
        return res;
    }

    public Comparator<Result> newComparator = new Comparator<Result>() {
        public int compare(Result a, Result b) {
            if (a.freq == b.freq) {
                return 0;
            }
            //-1是倒向排序， 1是正向排序
            return a.freq > b.freq ? -1 : 1;
        }    
    };
}

class Result {
    int val, freq;
    public Result(int val, int freq) {
        this.val = val;
        this.freq = freq;
    }
}