Write a PHP program which reads a list of pairs of a word and a page number, and prints the word and a list of the corresponding page numbers

<?php
$page = array();
while($line = fgets(STDIN)){
    list($a, $b) = explode(" ", trim($line));
    if(!isset($page[$a])){
        $page[$a] = array();
    }
    $page[$a][] = $b;
} 
ksort($page);
echo "The word and a list of the corresponding page numbers:\n";
foreach($page as $word => $arr){
    sort($arr, SORT_NUMERIC);
    echo $word."\n";
    echo implode($arr, " ")."\n";
}

?>