题目描述：
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:
解题思路：
使用HashMap计数
代码如下：
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(freqArray[i]);
}
return res;
}
}
Java [Leetcode 347]Top K Frequent Elements
原文：http://www.cnblogs.com/zihaowang/p/5723387.html