Visible_Dots_On_a_Die.php

<?php

/**
 * Your task is to return the number of visible dots on a die after it has been rolled(that means the total count of dots that would not be touching the table when rolled)
 * 
 * 6, 8, 10, 12, 20 sided dice are the possible inputs for "numOfSides"
 * 
 * topNum is equal to the number that is on top, or the number that was rolled.
 * 
 * for this exercise, all opposite faces add up to be 1 more than the total amount of sides 
 * Example: 6 sided die would have 6 opposite 1, 4 opposite 3, and so on. for this exercise, the 10 sided die starts at 1 and ends on 10.
 * 
 * Note: topNum will never be greater than numOfSides
 * 
 * */

 function totalAmountVisible(int $topNum, int $numOfSides): int {
  
    //Calcular la suma de todas las caras del dado.
    $suma = ($numOfSides * ($numOfSides + 1)) / 2;
    //Calcular el numero oculto
    $downNum = $numOfSides + 1 - $topNum;

    return $suma - $downNum;
  }