Huffman coding in php

huffman.php

<?php

function huffmannEncode($string) {
    $originalString = $string;
    $occurences = array();

    while (isset($string[0])) {
        $occurences[] = array(substr_count($string, $string[0]), $string[0]);
        $string = str_replace($string[0], '', $string);
    }

    sort($occurences);

    while (count($occurences) > 1) {
        $row1 = array_shift($occurences);
        $row2 = array_shift($occurences);
        $occurences[] = array($row1[0] + $row2[0], array($row1, $row2));
        sort($occurences);
    }
    
    $dictionary = [];
    fillDictionary($dictionary, is_array($occurences[0][1]) ? $occurences[0][1] : $occurences);
    
    $encoded = '';
    for($i = 0; $i < strlen($originalString); $i++) {
        $encoded .= $dictionary[$originalString[$i]];
    }

    return [
    	'code' => $encoded,
    	'dictionary' => $dictionary
    ];
}

function fillDictionary(&$dictionary, $data, $value = '') {
    if (!is_array($data[0][1])) {
        $dictionary[$data[0][1]] = $value.'0';
    } else {
        fillDictionary($dictionary, $data[0][1], $value.'0');
    }
    if (isset($data[1])) {
        if (!is_array($data[1][1])) {
            $dictionary[$data[1][1]] = $value.'1';
        } else {
            fillDictionary($dictionary, $data[1][1], $value.'1');
        }
    }
}

function huffmannDecode($encodedData, $dictionary) {
	$decoded = '';
    $currentCode = '';

    for ($i = 0; $i < strlen($encodedData); $i++) {
        $currentCode .= $encodedData[$i];

        foreach ($dictionary as $char => $code) {
            if ($code === $currentCode) {
                $decoded .= $char;
                $currentCode = '';
                break;
            }
        }
    }

    return $decoded;
}

$input = "salom dunyo";
echo "Input: {$input}\n";
$encodedData = huffmannEncode( $input );
echo "Encoded: {$encodedData['code']}\n";
$decodedData = huffmannDecode( $encodedData['code'], $encodedData['dictionary'] );
echo "Decoded: {$decodedData}\n";