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Guess the odds of drawing blue
<?php
/**
* Unit tests for Blue and Red Marbles game.
*
* @see https://www.codewars.com/kata/thinkful-number-drills-blue-and-red-marbles/
*
* You and a friend have decided to play a game to drill your statistical intuitions.
* The game works like this:
* You have a bunch of red and blue marbles.
* To start the game you grab a handful of marbles of each color and put them
* into the bag, keeping track of how many of each color go in.
* You take turns reaching into the bag, guessing a color, and then pulling one
* marble out. You get a point if you guessed correctly.
* The trick is you only have three seconds to make your guess,
* so you have to think quickly.
*
* You've decided to write a function, guess_blue() to help automatically calculate
* whether you should guess "blue" or "red". The function should take four arguments:
* the number of blue marbles you put in the bag to start
* the number of red marbles you put in the bag to start
* the number of blue marbles pulled out so far, and
* the number of red marbles pulled out so far.
*
* guess_blue() should return the probability of drawing a blue marble,
* expressed as a float.
*
* @package Cata\Tests\Unit\NumberDrills
* @author Caspar Green <caspar@iCasparWebDevelopment.com>
* @since 1.0.0
*/
declare(strict_types=1);
namespace Cata\Tests\Unit\NumberDrills;
use Cata\NumberDrills\GuessMarblesGame;
use PHPUnit\Framework\TestCase;
/**
* Class GuessMarblesGameTest
*
* @package Cata\Tests\Unit\NumberDrills
* @since 1.0.0
*/
class GuessMarblesGameTest extends TestCase
{
/**
* Test guessBlue() should return odds of drawing a blue marble.
*
* @since 1.0.0
*
* @return void
*/
public function testGuessBlueShouldReturnOddsWhenBlueAndRedMarbles(): void
{
$game = new GuessMarblesGame();
$this->assertEquals(0.0, $game->guessBlue(0, 0, 0, 0));
$this->assertEquals(0.6, $game->guessBlue(5, 5, 2, 3));
}
}
<?php
/**
* GuessMarbleGame class.
*
* @package Cata\NumberDrills
* @author Caspar Green <caspar@iCasparWebDevelopment.com>
* @since 1.0.0
*/
declare(strict_types=1);
namespace Cata\NumberDrills;
/**
* Class GuessMarblesGame
*
* @package Cata\NumberDrills
* @since 1.0.0
*/
class GuessMarblesGame
{
public function guessBlue(
int $initialBlue,
int $initialRed,
int $drawnBlue,
int $drawnRed
): float {
$remainingBlue = $initialBlue - $drawnBlue;
$remainingTotal = $remainingBlue + $initialRed - $drawnRed;
return $remainingTotal
? $remainingBlue / $remainingTotal
: 0;
}
}
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