Java [Leetcode 347]top K Frequent Elements

Title Description:

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

For example,
Given [1,1,1,2,2,3] and k = 2, return [1,2] .

Note:

• You may assume K are always valid, 1≤ k ≤number of unique elements.
• Your algorithm's time complexity must be better than O (n log n), where n is the array ' s size.

Problem Solving Ideas:

Using HashMap count

The code is as follows:

public class Solution {public    list<integer> topkfrequent (int[] nums, int k) {    Map<integer, integer> Map = new Hashmap<integer, integer> ();    list<integer>[] Freqarray = new List[nums.length + 1];        for (int num:nums) {        map.put (num, map.getordefault (num, 0) + 1);        }        for (int key:map.keySet ()) {        int freq = Map.get (key);        if (freqarray[freq] = = null)        Freqarray[freq] = new arraylist<integer> ();        Freqarray[freq].add (key);        }        list<integer> res = new arraylist<> ();        for (int i = freqarray.length-1; I >= 0 & Res.size () < K; i--) {        if (freqarray[i]! = null)        Res.addall (f Reqarray[i]);        }        return res;    }}

　　

Java [Leetcode 347]top K Frequent Elements