- var_dump: documentation ( source)
- array_keys: documentation ( source)
- preg_grep: documentation ( source)
- current: documentation ( source)
<?php
$array =array(
"123,456,789"=> "1,1,1",
"333"=>"1",
"777"=>"1"
);
$keys = array_keys($array);
$matching_key = preg_grep("/\b333\b/", $keys);
$value = $array[current($matching_key)];
var_dump($matching_key);