time conversion in 24 hrs hacker rank test

time_conversion.php

<?php

/*
 * Complete the 'timeConversion' function below.
 *
 * The function is expected to return a STRING.
 * The function accepts STRING s as parameter.
 */

function timeConversion($s) {
       
        $arr = explode(':', $s);

        $timeoftheday = strtolower(substr($s, 8));

        if ($timeoftheday  == 'pm') {
            if ($arr[0]  == '12') {

                $newStr = str_replace(substr($arr[2], 2), '', $arr[2]);
                $arr[2] = $newStr;
                return implode(':', $arr);
            }
            $r = $arr[0] + 12;
            $arr[0] = (string) $r;
            $newStr = str_replace(substr($arr[2], 2), '', $arr[2]);
            $arr[2] = $newStr;
            return implode(':', $arr);
        } elseif ($timeoftheday  == 'am') {
            if ($arr[0] == '12') {
                $arr[0] = '00';
            }
            $newStr = str_replace(substr($arr[2], 2), '', $arr[2]);
            $arr[2] = $newStr;

            return implode(':', $arr);
        }

}

$fptr = fopen(getenv("OUTPUT_PATH"), "w");

$s = rtrim(fgets(STDIN), "\r\n");

$result = timeConversion($s);

fwrite($fptr, $result . "\n");

fclose($fptr);