Fastest way to check if an array is sorted

Question

Considering there is an array returned from a function which is of very large size.

What will be the fastest approach to test if the array is sorted?

Answer 1

The question that comes to my mind is "why"?

Is it to avoid re-sorting an already-sorted list? If yes, just use Timsort (standard in Python and Java). It's quite good at taking advantage of an array/list being already sorted, or almost sorted. Despite how good Timsort is at this, it's better to not sort inside a loop.

Another alternative is to use a datastructure that is innately sorted, like a treap, red-black tree or AVL tree. These are good alternatives to sorting inside a loop.