迭代空列表的时间复杂度

Question

In the following code what would be the best case complexity? Is the best case input an empty list which means the loop doesn't iterate and therefore O(1)? Or should you consider it as a loop that always iterates n times and therefore O(n), regardless of input?

def f(L, x): 
    n = len(L) 
    c = 0 
    for i in range(n): 
        if L[i] == x: 
            c = c + 1 
    return c 

Answer 1

It would always be O(n), since no matter the input the loop will always iterate n times. N being equal to 1 would not make the complexity ever equal O(1), O(1) is reserved only for atomic operations that no matter what will be O(1).

Basically O(N) refers to the fact that this code snippet's time depends on N in a linear way.