1636. Sort Array by Increasing Frequency

Problem

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

Problem Summary

Given an integer array nums, sort the array in ascending order by the frequency of each value. If multiple values have the same frequency, sort them in descending order by their values. Return the sorted array.

Solution Approach

• Easy problem. First count the frequency of each value, then sort by frequency in ascending order. For values with the same frequency, sort by value in descending order.

Code

package leetcode

import "sort"

func frequencySort(nums []int) []int {
	freq := map[int]int{}
	for _, v := range nums {
		freq[v]++
	}
	sort.Slice(nums, func(i, j int) bool {
		if freq[nums[i]] == freq[nums[j]] {
			return nums[j] < nums[i]
		}
		return freq[nums[i]] < freq[nums[j]]
	})
	return nums
}