Looks like you're trying to access an element outside the list range (basically you're using an invalid index)

Answered above

I compared your solution with other solutions to see if you were right:

Random test: N = 7, REFERENCE LIST = [16,22,15,20,23,12,23,13,3,20,12,8,7,3,16,13,19,18,18,24,6,20,16,23,2,12,25,20,16,17];

arpegx: [16,2,17,20,23,12,25]
henrikgebauer: [20,25,17,2,16,12,23]
sneeb123: [20,25,17,2,16,12,23]
Reference solution: [20,25,17,2,16,12,23]

Assertion message:
N = 7, REFERENCE LIST = [16,22,15,20,23,12,23,13,3,20,12,8,7,3,16,13,19,18,18,24,6,20,16,23,2,12,25,20,16,17]:
Failed asserting that two arrays are identical.
Expected: Array &0 (
    0 => 20
    1 => 25
    2 => 17
    3 => 2
    4 => 16
    5 => 12
    6 => 23
)
Actual  : Array &0 ()

I don't have a PHP solution of my own because the translation was made by another user and approved by another one, but I think the issue is in your solution. Let me know if everything checks out!

Edit: don't mind the "Actual" part of the assertion message, I ran the test without an algorithm so I just got a random test to use, but you can see from that "Expected" that the order is right

Hi! What language? And what test?

trashy_incel is right, the LRU queue updates are not shown in the example

Fixed, but I'd suggest to make the description language-agnostic to avoid these kinds of situations. Sorry again!

I'll update it real quick right now

Shoot, I forgot to update the description and as soon as I started updating it the translation got approved. Sorry for the inconvenience! Let me know if you want me to update it

Dart translation

Approved by someone

Python update (new testing framework)