While working on a PHP project, I came across the concepts of data structures and time complexity. I understand (maybe) basic cases like:

• Searching in an unsorted array with a loop takes O(n) in the worst
  case.
• Nested loops (e.g., a loop inside another loop) result in O(n²)
  complexity.

I am looking for resources or methods to determine the time complexity of built-in PHP functions.

For instance, what is the time complexity of array_count_values($array)?

If it is O(n²), then an alternative approach could be:
Sorting the array first sort($array) → O(n logn). Iterating through it once O(n) to count occurrences. This would result in O(n log n) + O(n) = O(n log n) in total. Would this be a more efficient approach ?

Questions:

1. Is there an official way to determine the time complexity of PHP
   built-in functions?

2. Are there any references (documentation, source code, or empirical analysis) to study this?

3. Can you suggest beginner-friendly resources for understanding time
   complexity and data structure ?

Any insights or resources would be greatly appreciated.