RankTransformOfArray.php

<?php

namespace App;

/**
 * Rank Transform of an Array
 *
 * Given an array of integers arr, replace each element with its rank. The rank represents how large the element is.
 * The rank has the following rules:
 * - Rank is an integer starting from 1.
 * - The larger the element, the larger the rank. If two elements are equal, their rank must be the same.
 * - Rank should be as small as possible.
 *
 * Example 1:
 * Input: arr = [40,10,20,30]
 * Output: [4,1,2,3]
 * Explanation: 40 is the largest element. 10 is the smallest. 20 is the second smallest. 30 is the third smallest.
 *
 * Example 2:
 * Input: arr = [100,100,100]
 * Output: [1,1,1]
 * Explanation: Same elements share the same rank.
 *
 * Example 3:
 * Input: arr = [37,12,28,9,100,56,80,5,12]
 * Output: [5,3,4,2,8,6,7,1,3]
 *
 * https://leetcode.com/problems/rank-transform-of-an-array/description
 */
class RankTransformOfArray
{
    /**
     * @param int[] $arr
     * @return int[]
     */
    public function arrayRankTransform(array $arr): array
    {
        $sorted = $arr;
        sort($sorted);
        $ranks = [];
        $rank = 1;
        foreach ($sorted as $value) {
            if (!isset($ranks[$value])) {
                $ranks[$value] = $rank++;
            }
        }
        $result = [];
        foreach ($arr as $value) {
            $result[] = $ranks[$value];
        }
        return $result;
    }
}