LeetCode #347. Top K Frequent Elements

题目要求：

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].

即求出线最频繁的前K个数。要求时间复杂度不大于O(nlogn).明显就是先hash存起来，然后排序，拿到前k个值即可。写的不是很好，如果有更好的算法实现请接评论

public List<Integer> topKFrequent(int[] nums, int k) {
ArrayList<Integer> kFrequent = new ArrayList<Integer>();
HashMap<Integer, Integer> cacheMap = new HashMap<Integer, Integer>();
for (int i : nums) {
if (!cacheMap.containsKey(i)) {
cacheMap.put(i, 1);
continue;
}
int count = cacheMap.get(i) + 1;
cacheMap.put(i, count);
}
ArrayList<Map.Entry<Integer,Integer>> list = new ArrayList<Map.Entry<Integer, Integer>>(cacheMap.entrySet());
Collections.sort(list, new Comparator<Map.Entry<Integer, Integer>>() {
@Override
public int compare(Map.Entry<Integer, Integer> o1, Map.Entry<Integer, Integer> o2) {
return o2.getValue() - o1.getValue();
}
});
int count = 0;
while (count++ < k)
kFrequent.add(list.get(count).getKey());
return kFrequent;
}