Link: https://leetcode.cn/problems/top-k-frequent-elements/
Question
difficulty: mid
adj diff: 3
Given an integer array nums and an integer k, return the k most frequent elements. You may return the answer in any order.
Example 1:
Input: nums = [1,1,1,2,2,3], k = 2
Output: [1,2]
Example 2:
Input: nums = [1], k = 1
Output: [1]
Constraints:
1 <= nums.length <= 105
-104 <= nums[i] <= 104
k is in the range [1, the number of unique elements in the array].
It is guaranteed that the answer is unique.
Follow up: Your algorithm's time complexity must be better than O(n log n), where n is the array's size.
Code
class Solution {
public int[] topKFrequent(int[] nums, int k) {
Map<Integer, Integer> map = new HashMap<Integer, Integer>();
for (int i: nums) {
map.put(i,
map.getOrDefault(i, 0) + 1
);
}
PriorityQueue<Integer> heap = new PriorityQueue<Integer>(new Comparator<Integer>() {
public int compare(Integer m, Integer n) {
return map.get(m) - map.get(n);
}
});
for (int i: map.keySet()) {
heap.offer(i);
if (heap.size() > k) {
heap.poll();
}
}
int[] ans = new int[k];
for (int i = 0; i < k; i++) {
ans[i] = heap.poll();
}
return ans;
}
}