1636. Sort Array by Increasing Frequency

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:

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

 

Solutions

Solution: Hash Map

• Time complexity: O(nlogn)
• Space complexity: O(n)

 

JavaScript

/**
 * @param {number[]} nums
 * @return {number[]}
 */
const frequencySort = function (nums) {
  const frequencyMap = nums.reduce((map, num) => {
    const count = map.get(num) ?? 0;

    return map.set(num, count + 1);
  }, new Map());

  return nums.sort((a, b) => frequencyMap.get(a) - frequencyMap.get(b) || b - a);
};