Problem description:

Given an array of integers nums, sort the array in increasing order based on the frequency of the values. If multiple values have the same frequency, sort them in decreasing order.

Return the sorted array.

Example 1:

1
2
3
Input: nums = [1,1,2,2,2,3]
Output: [3,1,1,2,2,2]
Explanation: '3' has a frequency of 1, '1' has a frequency of 2, and '2' has a frequency of 3.

Example 2:

1
2
3
Input: nums = [2,3,1,3,2]
Output: [1,3,3,2,2]
Explanation: '2' and '3' both have a frequency of 2, so they are sorted in decreasing order.

Example 3:

1
2
Input: nums = [-1,1,-6,4,5,-6,1,4,1]
Output: [5,-1,4,4,-6,-6,1,1,1]

Constraints:

  • 1 <= nums.length <= 100
  • 100 <= nums[i] <= 100

Solution:

Use hash table to count frequency.
sort with lambda function, notice if frequency is the same we want to sort decreasing.

1
2
3
4
5
6
7
8
9
class Solution:
    def frequencySort(self, nums: List[int]) -> List[int]:
        freq = defaultdict(int)
        for n in nums:
            freq[n] += 1
        
        res = sorted(nums, key=lambda x: (freq[x], -x))
        print(res)
        return res

time complexity: $O(nlongn)$
space complexity: $O(n)$
reference:
related problem: