SortArrayByIncreasingFrequency.php

<?php

namespace App;

/**
 * Sort Array by Increasing Frequency
 *
 * 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]
 *
 * https://leetcode.com/problems/sort-array-by-increasing-frequency
 */
class SortArrayByIncreasingFrequency
{
    /**
     * @param int[] $nums
     * @return int[]
     */
    public function frequencySort(array $nums): array
    {
        arsort($nums);

        /** @var array<array-key, int> $arr */
        $arr = array_count_values($nums);
        asort($arr);

        usort($nums, static function (int $a, int $b) use ($arr) {
            $a = $arr[$a];
            $b = $arr[$b];
            return $a <=> $b;
        });

        return $nums;
    }
}