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

coin_change.php

<?php

function coin_change($amount) {
    // What us British use...
    $coinDenominations = array(
        'Fifty pence'  => 50,
        'Twenty pence' => 20,
        'Ten pence'    => 10,
        'Five pence'   => 5,
        'Two pence'    => 2,
        'One penny'    => 1
    );

    // Will hold the final amounts
    $change = array();

    foreach ($coinDenominations 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;
}

TestCoinChange.php

<?php

// Just a PHPUnit test case for this function. Passes on 3.6.10 of PHPUnit.

public function testCoinChange()
{
    $testStub = array(
        99 => array(1, 2, 0, 1, 2, 0),
        50 => array(1, 0, 0, 0, 0, 0),
        3 => array(0, 0, 0, 0, 1, 1),
        8 => array(0, 0, 0, 1, 1, 1),
        1 => array(0, 0, 0, 0, 0, 1),
        41 => array(0, 2, 0, 0, 0, 1),
        36 => array(0, 1, 1, 1, 0, 1),
    );

    foreach($testStub as $amount => $stub) {
        $this->assertEquals($stub, array_values(coin_change($amount)));
    }

}