FindLuckyIntegerInArray.php

<?php

namespace App;

/**
 * Find Lucky Integer in an Array
 *
 * Given an array of integers arr, a lucky integer is an integer that has a frequency in the array equal to its value.
 * Return the largest lucky integer in the array. If there is no lucky integer return -1.
 *
 * Example 1:
 * Input: arr = [2,2,3,4]
 * Output: 2
 * Explanation: The only lucky number in the array is 2 because frequency[2] == 2.
 *
 * Example 2:
 * Input: arr = [1,2,2,3,3,3]
 * Output: 3
 * Explanation: 1, 2 and 3 are all lucky numbers, return the largest of them.
 *
 * Example 3:
 * Input: arr = [2,2,2,3,3]
 * Output: -1
 * Explanation: There are no lucky numbers in the array.
 *
 * https://leetcode.com/problems/find-lucky-integer-in-an-array
 */
class FindLuckyIntegerInArray
{
    /**
     * @param int[] $arr
     * @return int
     */
    public function findLucky(array $arr): int
    {
        $result = -1;
        $count = array_count_values($arr);
        foreach ($count as $key => $value) {
            if ($key === $value && $key > $result) {
                $result = $key;
            }
        }
        return $result;
    }
}