cashmachine.php

<?php

namespace Obiz\Challenges\CashMachine;

class WithdrawException extends \Exception {
    
}

class CashMachine {

    /**
     * Available bill values in the ATM. Consider quantities are unlimited.
     */
    private $bills = array(2, 5, 10, 20, 50, 100);
    private $money_left;
    private $cash = array();

    function __construct() {
        rsort($this->bills);
    }

    /**
     * Returns the bills that should be distributed for a given withdraw amount and available bills,
     * MINIMIZING the total number of distributed bills.
     * Ex: getBills(72) => array(2 => 1, 20 => 1, 50 => 1).
     *
     * @param int $withdrawAmount How much we want to withdraw from the ATM
     * @throws WithdrawException if the exact amount cannot be gathered with the available bills.
     * @return array Associative array representing the bills that should be distributed by the cash machine.
     */
    public function getBills($withdrawAmount) {
        $this->cash = array();
        $this->money_left = $withdrawAmount;
        while ($this->money_left > 0) {
            if ($this->money_left < min($this->bills)) {
                throw new WithdrawException('This amount cannot be paid.');
            }
            $bill = $this->configureBills();
            $this->cash[] = $bill;
            $this->money_left -= $bill;
        }
        return array_count_values($this->cash);
    }

    private function configureBills() {
        foreach ($this->bills as $bill) {
            $division = $this->money_left / $bill;
            $rest = $this->money_left % $bill;
            if ( ($division >= 1) && ( $rest > (min($this->bills)+1) || ($rest === min($this->bills)) || ($rest === 0) ) ) {
                return $bill;
            }
        } 
        return min($this->bills);
    }

}

$atm = new CashMachine;
print_r($atm->getBills(52));