问题
I am wondering about the time complexity of the get operation of deque in Python.
I know that it is implemented as a doubly link in Python. Does that mean that its time complexity is O(n)?
回答1:
deque are implemented a little smarter than just doubly-linked lists. They're a doubly-linked list of blocks of Python objects, where the left and right sides may be incomplete blocks.
The Big-O cost of accessing in the middle is still O(n), but it has a constant divisor (implementation dependent, CPython 3.5 allocates blocks that can store 64 objects). So if your deque has 1000 members, accessing in the middle still involves only around 7-8 "linked list-style" traversals, not 500-some. If the deque is smallish (65 to 128 elements, depending on how the empty slots align with the head and tail blocks), then lookup of any element is equal cost.
来源：https://stackoverflow.com/questions/39522787/time-complexity-of-random-access-in-deque-in-python