deque

Confusion on iterators invalidation in deque

由 旧街凉风 提交于 2019-11-27 22:10:40
问题 I'm bit confused regarding iterator invalidation in deque. (In the context of this question) Following is the excerpts from -- The C++ Standard Library: A Tutorial and Reference, By Nicolai M. Josuttis Any insertion or deletion of elements other than at the beginning or end invalidates all pointers, references, and iterators that refer to elements of the deque. Following is the excerpts from SGI site: The semantics of iterator invalidation for deque is as follows. Insert (including push_front

Use slice notation with collections.deque

由 给你一囗甜甜゛ 提交于 2019-11-27 19:59:47
How would you extract items 3..6 efficiently, elegantly and pythonically from the following deque without altering it: from collections import deque q = deque('',maxlen=10) for i in range(10,20): q.append(i) the slice notation doesn't seem to work with deque ... import itertools output = list(itertools.islice(q, 3, 7)) For example: >>> import collections, itertools >>> q = collections.deque(xrange(10, 20)) >>> q deque([10, 11, 12, 13, 14, 15, 16, 17, 18, 19]) >>> list(itertools.islice(q, 3, 7)) [13, 14, 15, 16] This should be more efficient the the other solutions posted so far. Proof? [me

Time complexity of removing items in vectors and deque

由 别说谁变了你拦得住时间么 提交于 2019-11-27 17:32:00
问题 I have read that time complexity of adding items to end of a std::vector is amortized constant and inserting items at the top and bottom of a std::deque is constant.Since both these containers have a random access iterator thus accessing elements at any index is constant. Please let me know if I have any of these facts wrong.My question is if accessing an element in a std::vector or std::deque is constant then why is the time complexity of removing an element via erase O(n). One of the

Why does push_back or push_front invalidate a deque's iterators?

由 守給你的承諾、 提交于 2019-11-27 15:40:07
问题 As the title asks. My understanding of a deque was that it allocated "blocks". I don't see how allocating more space invalidates iterators, and if anything, one would think that a deque's iterators would have more guarantees than a vector's, not less. 回答1: The C++ standard doesn't specify how deque is implemented. It isn't required to allocate new space by allocating a new chunk and chaining it on to the previous ones, all that's required is that insertion at each end be amortized constant

Why typical Array List implementations aren't double-ended?

由 对着背影说爱祢 提交于 2019-11-27 07:48:53
问题 Why aren't ArrayList s generally implemented to be double-ended, which would support fast amortized insertion in the front as well as the back? Is there ever a disadvantage to using the latter over the former? (I'm not talking just about Java -- I haven't seen double-ended array lists being the default in any other language, but Java was just a good example here.) *Edit: I originally called them "array deques" but that was a misunderstanding on my part; I wasn't talking about queues, but

Is this deque thread-safe in python?

由 回眸只為那壹抹淺笑 提交于 2019-11-27 06:51:11
问题 I can't decide whether the following deque is thread-safe. In short, I've created a class with a deque that displays its contents every 1 sec in a new thread (so it won't pause the main program while printing). The deque is filled from the main thread, so basically there SHOULD be a chance of collision. HOWEVER, the deque is filled using a class method, so essentially it is accessed from within the instance itself, therefore from the same thread. Here's the simplified code: import threading

Java equivalent of std::deque

由 人走茶凉 提交于 2019-11-27 05:55:56
问题 I'm a relatively new Java programmer coming from C++/STL, and am looking for a class with these characteristics (which the C++ std::deque has, as I understand it): O(1) performance for insertion/removal at the beginning/end O(1) performance for lookup by index are growable collections (don't need fixed size bounds) Is there a Java equivalent to this? I found the Java 1.6 [ArrayDeque] class which has the insert/removal and growable characteristics, but don't seem to have lookup-by-index unless

Why is ArrayDeque better than LinkedList

由 余生颓废 提交于 2019-11-27 05:53:16
I am trying to to understand why Java's ArrayDeque is better than Java's LinkedList as they both implement Deque interface. I hardly see someone using ArrayDeque in their code. If someone sheds more light into how ArrayDeque is implemented, it would be helpful. If I understand it, I will be more confident using it. I could not clearly understand the JDK implementation as to the way it manages head and tail references. Linked structures are possibly the worst structure to iterate with a cache miss on each element. On top of it they consume way more memory. If you need add/remove of the both

Use slice notation with collections.deque

由 核能气质少年 提交于 2019-11-27 04:27:05
问题 How would you extract items 3..6 efficiently, elegantly and pythonically from the following deque without altering it: from collections import deque q = deque('',maxlen=10) for i in range(10,20): q.append(i) the slice notation doesn't seem to work with deque ... 回答1: import itertools output = list(itertools.islice(q, 3, 7)) For example: >>> import collections, itertools >>> q = collections.deque(xrange(10, 20)) >>> q deque([10, 11, 12, 13, 14, 15, 16, 17, 18, 19]) >>> list(itertools.islice(q,

Why would I prefer using vector to deque

由 不问归期 提交于 2019-11-27 02:45:42
Since they are both contiguous memory containers; feature wise, deque has almost everything vector has but more, since it is more efficient to insert in the front. Why whould anyone prefer std::vector to std::deque ? phooji Elements in a deque are not contiguous in memory; vector elements are guaranteed to be. So if you need to interact with a plain C library that needs contiguous arrays, or if you care (a lot) about spatial locality, then you might prefer vector . In addition, since there is some extra bookkeeping, other ops are probably (slightly) more expensive than their equivalent vector
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