Get the lowest amount of coins for a given change value.

ntd-coin-changer.php

<?php

function change_make($price, $pay)
{
    if ($price === 0 || $pay === 0 || $price > $pay) {
        return;
    }

    $change = $pay - $price;

    return change_coins($change);
}

// Copied from https://gist.github.com/samvaughton/7354168
function change_coins($amount)
{
    // Use NTD coins
    $denominations = [
        'fifty dollars' => 50,
        'ten dollars' => 10,
        'five dollars' => 5,
        'one dollar' => 1,
    ];

    // Will hold the final amounts
    $change = [];

    foreach ($denominations as $name => $value) {
        // Get the max number of times this coin denomination can fit into the amount
        $coins = floor($amount / $value);

        // Record the amount of coins for that denomination
        $change[$name] = $coins;

        // If 1 or more of the denomination can fit into the amount
        if ($coins > 0) {
            // Then minus that value of the total amount
            $amount -= ($value * $coins);
        }
    }

    return $change;
}

print_r(change_make(100, 110));  // [0, 1, 0, 0]
print_r(change_make(50, 50));  // [0, 0, 0, 0]
print_r(change_make(50, 66));  // [0, 1, 1, 1]
print_r(change_make(10, 11));  // [0, 0, 0, 1]
print_r(change_make(1, 10));  // [0, 0, 1, 4]