LeetCode 347. Top K Frequent Elements

Source: https://leetcode.com/problems/top-k-frequent-elements/

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

Example 1:

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

Example 2:

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

Note:

  • You may assume k is 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.

We use a hashmap to count every number. Then we transform this hashmap to a list, and sort it, output the first k elements.

Github: https://github.com/tinyfool/leetcode/tree/master/src/p0347

To see more hashtable related problems, see 
Problems and Solutions of Hashmap.

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