How find difference of the two array
// ARRAY 1
$a1 = array(
    "a1" => 1,
    "a3" => array(
        "a31" => 31
    ),
    "a4" => array(
        "a41" => 41
    ),
    "a5" => array(
        "a51" => 51,
        "a52" => 52
    )
);
// ARRAY 2
$a2 = array(
    "a1" => 1,
    "a2" => 2,
    "a3" => array(
        "a31" => 31,
        "a32" => array(
            "a321" => 321,
            "a322" => 322
        )
    ),
    "a4" => array(
        "a41" => 42
    ),
    "a5" => array(
        "a51" => 51,
        "a52" => 52
    )
);
array_diff function returns ==> Array ( ) 
But there is a lot of difference exist in the above two array variables.
example:
- in ARRAY1 There is no key a2 but in ARRAY2 a2 is available.
 - ARRAY2 a3 contain nested array (one nested level ) but in ARRAY 2 contain two nested sub level.
 
So here i want to compare two array n-level (ie. nested array)