how to Grouping array in php

I would like to know how to combine and overwrite the already existed array value in php.

my current array look like:

Array
(
    [1149] => 3
    [4108] => 5
)

As shown above values, i need expected result in php as below :

Array
(
    [0] => Array
        (
            [offer_id] => 1149
            [quantity] => 3
        )

    [1] => Array
        (
            [offer_id] => 4108
            [quantity] => 5
        )
)

Solution:

How about:

$result = [];
foreach (
    [
        1149 => 3,
        4108 => 3,
    ] as $key => $value
) {
    $result[] = [
        'offer_id' => $key,
        'quantity' => $value,
    ];
}

print_r($result);