CountDistinctNumbersOnBoard.php

<?php

namespace App;

/**
 * Count Distinct Numbers on Board
 *
 * You are given a positive integer n, that is initially placed on a board. Every day, for 10^9 days, you perform the
 * following procedure:
 * - For each number x present on the board, find all numbers 1 <= i <= n such that x % i == 1.
 * - Then, place those numbers on the board.
 * Return the number of distinct integers present on the board after 10^9 days have elapsed.
 * Note:
 * - Once a number is placed on the board, it will remain on it until the end.
 * - % stands for the modulo operation. For example, 14 % 3 is 2.
 *
 * Example 1:
 * Input: n = 5
 * Output: 4
 * Explanation: Initially, 5 is present on the board.
 * The next day, 2 and 4 will be added since 5 % 2 == 1 and 5 % 4 == 1.
 * After that day, 3 will be added to the board because 4 % 3 == 1.
 * At the end of a billion days, the distinct numbers on the board will be 2, 3, 4, and 5.
 *
 * Example 2:
 * Input: n = 3
 * Output: 2
 * Explanation:
 * Since 3 % 2 == 1, 2 will be added to the board.
 * After a billion days, the only two distinct numbers on the board are 2 and 3.
 *
 * https://leetcode.com/problems/count-distinct-numbers-on-board
 */
class CountDistinctNumbersOnBoard
{
    /**
     * @param int $n
     * @return int
     */
    public function distinctIntegers(int $n): int
    {
        $count = 1;
        for ($i = $n; $i > 0; $i--) {
            if ($n % $i === 1) {
                return $this->distinctIntegers($i) + 1;
            }
        }
        return $count;
    }
}