coinChallenge

<?php

    $coins = [1, 2];
    $totalAmount = 4;

    function calculateCombo(array $coins, int $amount, int $currentindex)
    {
        if($amount == 0) { return 1; }

        if($amount < 0) { return 0; }

        $combos = 0;
        for($i = $currentindex; $i < count($coins); $i++)
        {
            $combos = $combos + calculateCombo($coins, $amount - $coins[$i], $i);
        }

        return $combos;
    }

    echo calculateCombo($coins, $totalAmount, 0);
?>