方法1: 声明新的类 ＋ hashmap ＋ priority queue

 

1 class Solution { 2     public List
     
       topKFrequent(int[] array, int k) { 3         Queue
      
        queue = new PriorityQueue
       
        (newComparator); 4         Map
        
          map = new HashMap<>(); 5         for (int i = 0; i < array.length; i++) { 6             if (map.containsKey(array[i])) { 7                 map.put(array[i], map.get(array[i]) + 1); 8             } else { 9                 map.put(array[i], 1);10             }11         }12         for(int i : map.keySet()) {13             queue.offer(new Result(i, map.get(i)));14         }15 16         List
         
           res = new ArrayList<>();17         for (int i = 0; i < k; i++) {18             res.add(queue.poll().val);19         }20         return res;21     }22 23     public Comparator
          
            newComparator = new Comparator
           
            () {24 public int compare(Result a, Result b) {25 if (a.freq == b.freq) {26 return 0;27 }28 //-1是倒向排序， 1是正向排序29 return a.freq > b.freq ? -1 : 1;30 } 31 };32 }33 34 class Result {35 int val, freq;36 public Result(int val, int freq) {37 this.val = val;38 this.freq = freq;39 }40 }