347-top-k-frequent-elements

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Description

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
• 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.

Solution(Python)

class Solution:
    def topKFrequent(self, nums: List[int], k: int) -> List[int]:
        return self.prioirtyQueue(nums, k)

    # Time Complexity: O(nlogn)
    # Space Complexity: O(n)
    def naive(self, nums: List[int], k: int) -> List[int]:
        freqmap = Counter(nums)
        freqmap = sorted(freqmap, key=freqmap.get, reverse=True)
        return freqmap[:k]

    # Time Complexity: O(nlogk)
    # Space Complexity: O(n)
    def prioirtyQueue(self, nums: List[int], k: int) -> List[int]:
        if k == len(nums):
            return nums

        count = Counter(nums)

        return heapq.nlargest(k, count.keys(), key=count.get)