Top K Frequent Elements
Problem
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] <= 104kis 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
- HashMap & BucketSort
- Time: O(n)
- Space: O(n)
class Solution(object):
def topKFrequent(self, nums, k):
"""
:type nums: List[int]
:type k: int
:rtype: List[int]
"""
count = {}
freq = [[] for i in range(len(nums) + 1)]
for n in nums:
count[n] = 1 + count.get(n, 0)
for n, c in count.items():
freq[c].append(n)
res = []
for i in range(len(freq) - 1, 0, -1):
for n in freq[i]:
res.append(n)
if len(res) == k:
return res