cto-challenge-level1.php

<?php

/**
 * クーポン自体が独立しているから順次処理していく感じにした
 * @param array $amount
 * @param array $myCouponList
 * @return array
 */
function selectOptimalCoupons($amount, $myCouponList){
    $hydrate = function($coupons){
        $hydrated = [];
        foreach($coupons as $discount)
        {
            if( array_key_exists($discount, $hydrated) )
            {
                $hydrated[$discount]++;
            }
            else
            {
                $hydrated[$discount] = 1;
            }
        }
        return $hydrated;
    };
    $sortByDiscount = function(array $hydrated)
    {
        $sorted   = $hydrated;
        krsort($sorted);
        return $sorted;
    };
    $countUp = function($amount, array $sortedCoupons)
    {
        $usedCoupons = array_fill_keys(array_keys($sortedCoupons), 0);
        foreach( $sortedCoupons as $discount => $nCoupon )
        {
            while($amount >= $discount && ($nCoupon - $usedCoupons[$discount]) > 0)
            {
                $amount -= $discount;
                $usedCoupons[$discount]++;
            }

        }
        return $usedCoupons;
    };

    $hydrated   = $hydrate($myCouponList);
    $sorted     = $sortByDiscount($hydrated);
    $usedCoupons = $countUp($amount, $sorted);

   return $usedCoupons;
}

$test = [
    [
        'amount' => 100,
        'couponList' => [],
    ],
    [
        'amount' => 100,
        'couponList' => [
            50,
            50,
            100,
        ],
    ],
    [
        'amount' => 470,
        'couponList' => [
            50,
            50,
            50,
            100,
            100,
            100,
            100,
            100,
            500,
        ],
    ],
    [
        'amount' => 1230,
        'couponList' => [
            50,
            50,
            50,
            50,
            50,
            50,
            100,
            100,
            100,
            100,
            100,
            500,
            500,
        ],
    ],
];

foreach( $test as $case )
{
    print_r(
        selectOptimalCoupons(
            $case['amount'],
            $case['couponList']
        )
    );
}