How to group arrays?

Question

PHP

There is such an array that shows empty regions in a file (where no data is written):

[
[100,150],
[0,10],
[11,20],
...
[500,750]
]

That is, an array with arrays... so it will be clearer: list($begin,$end)=$arr[0];..
How can you group its elements so that if there are 2 empty spaces that go in a row, they occupy 1 element, and not 2 different ones?
That is, from the array in the example, you need to get the following output:

[
[100,150],
[0,20],
...
[500,750]
]

?
Clarification - it is necessary that any number of consecutive regions be combined into 1 region. But if at least 1 byte is occupied between them, then they should not connect