PHP solution for https://www.hackerrank.com/challenges/sock-merchant/

sock-merchant.php

<?php

$exampleArray = [9, 10 , 20 , 20 ,10 ,10 ,30 ,50 ,10 ,20];
$len = count($exampleArray);
    
echo sockMerchant($len, $exampleArray);

// Assumptions for sockMerchant function:
// 1. $n is the actual size of $ar (derived from count($ar))
// 2. $ar values are:
//     2.a. Valid ( 1 <= a[i] <= 100 ) 
//     2.b. Integers ( gettype(a[i]) === 'integer' ) | i: 0 to $n
function sockMerchant($n, $ar) {
	if (gettype($n) !== 'integer' || !$n) {
		return 0;
	}

	function getPairs($carry, $socks) {
		return $carry += floor($socks / 2);
	}

	$matchingSocks = array_count_values($ar);

	return array_reduce($matchingSocks, "getPairs");
}

?>