Find intersection of array

array-intersection.php

$arr1 = ['a', 'b', 'c'];
$arr2 = ['b', 'c', 'd'];
$intersectionArray = [];
foreach($arr2 as $key => $char) {
	$arr2[$char] = $char;
	unset($arr2[$key]);
}
foreach($arr1 as $char) {
	if(isset($arr2[$char])) {
		$intersectionArray[] = $char;	
	}
}

echo implode(',', $intersectionArray);

find-needle.php

//apple ale
//apple ael
function find($haystack, $needle) : bool {
	$arrayStr = str_split($haystack);
	$arrayNeedle = str_split($needle);
	$needleIndex = 0;
	$needleSize = count($arrayNeedle);
	$isFound = true;
	foreach($arrayStr as $char) {
		if($needleIndex == $needleSize) {
			break;
		} else if ($char == $arrayNeedle[$needleIndex]) {
			$needleIndex++;
		}
	}
	$isFound = $needleIndex == $needleSize;
	return $isFound;
}

echo (find('apple', 'ale') ? 'true' : 'false');