Leetcode347 Top K Frequent Elements

题目描述

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

Example 1:

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

Example 2:

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

思路

首先使用hashmap统计词频，用priorityqueue按照词频排序，priorityqueue采用参数为数组。

代码

class Solution {
    public int[] topKFrequent(int[] nums, int k) {
        if(nums.length==0||nums.length==1) return nums;
        int[] result = new int[k];
        HashMap<Integer,Integer> map = new HashMap<>();
        for(int i=0;i<nums.length;i++){
            if(map.containsKey(nums[i]))
                map.put(nums[i],map.get(nums[i])+1);
            else
                map.put(nums[i],1);
        }
        Queue<int[]> q = new PriorityQueue<int[]>((a,b)->a[0]-b[0]);
        for(Integer num : map.keySet()){
            q.add(new int[]{map.get(num),num});
            if(q.size()>k) q.poll();
        }
        for(int n=0;n<k;n++){
            int[] tmp = q.poll();
            result[n] = tmp[1];
        }
        
        return result;
    }
}