1636. Sort Array by Increasing Frequency

Problem Link

Description

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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:

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:

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:

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

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C++

class Solution {
public:
    vector<int> frequencySort(vector<int>& nums) {
        unordered_map<int, int> count;
 
        for (int x: nums) count[x]++;
 
        sort(nums.begin(), nums.end(), [&](int a, int b){
            if (count[a] == count[b]) return a > b;
            
            return count[a] < count[b];
        });
 
        return nums;
    }
};

Python3

class Solution:
    def frequencySort(self, nums: List[int]) -> List[int]:
        c = collections.Counter(nums)
        c = sorted(c.items(), key = lambda x : (x[1],-x[0]))
 
        res = []
        
        for key,value in c:
            for _ in range(value):
                res.append(key)
        
        return res