Deque | ended queue , which provides O indexed access
kandi X-RAY | Deque Summary
kandi X-RAY | Deque Summary
A double-ended queue, which provides O(1) indexed access, O(1) removals from the front and back, amortized O(1) insertions to the front and back, and O(N) insertions and removals anywhere else.
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QUESTION
std::deque is contiguous memory container or not ?
The famous book Effective STL by Scott Meyers says like below
Contiguous-memory containers (also known as array-based containers] store their elements in one or more (dynamically allocated) chunks of memory, each chunk holding more than one container element. If a new element is inserted or an existing element is erased, other elements in the same memory chunk have to be shifted up or down to make room for the new element or to fill the space formerly occupied by the erased element. This kind of movement affects both performance (see Items 5 and 14) and exception safety (as we'll soon see). The standard contiguous-memory containers are vector, string, and deque. The nonstandard rope is also a contiguous-memory container.
But you can find opposite explanation in cppreference.com
As opposed to std::vector, the elements of a deque are not stored contiguously: typical implementations use a sequence of individually allocated fixed-size arrays, with additional bookkeeping, which means indexed access to deque must perform two pointer dereferences, compared to vector's indexed access which performs only one.
Which one is true ?
...ANSWER
Answered 2022-Apr-07 at 14:39There is no conflict between the two quotes. Scott uses the term "contiguous container" in a sense a little wider than you might have seen it used elsewhere.
Scott writes (emphasize mine):
Contiguous-memory containers (also known as array-based containers] store their elements in one or more (dynamically allocated) chunks of memory, [...]
As the quote from cppref states, std::deque uses multiple arrays to store the elements. Within each array the elements are contiguous. Scott does not claim that all elements in a std::deque are contiguous in one chunk of memory.
QUESTION
I have created a custom memory allocator. To use it with STL Containers, I've also created a wrapper so that it adheres to the std::allocator_traits requirements.
ANSWER
Answered 2022-Apr-05 at 06:38If you can't change CustomAlloc code as Ted Lyngmo suggested, the alternative is to define CustomQueue as a subclass of std::queue:
QUESTION
Suppose we have a situation where we need FIFO data structure. For example, consume some events in the order they came in.
Additionally, we need to clear the entire queue from time to time.
std::queue seems like the perfect fit for doing that, but unfortunately it lacks a function for clearing the container.
So at this point, we have 2 alternatives:
std::queue
- we asked the STL lib what we need. Granted, the STL lib will give us more: it will give us an
std::dequedisguised as astd::queue - we got back only a part from what we need, namely the pop front and push back but without clear
- we will have to "emulate" clear somehow, without the naive way of looping and popping
std::deque
- we asked the STL lib what we need
- we got back what we asked for, but we've got too much: we also got push front and pop back
Overall, we either received too few or too much, never exactly what we really wanted.
Here is the thing that took me by surprise, while I was trying to provide clear functionality for using with std::queue which is a member var of my object
ANSWER
Answered 2022-Mar-31 at 14:40To clear the queue, you can also simply write
QUESTION
This is part of my doubly linked list deque python code.
The 'appendleft' function written almost similar to the 'append' function is normally output. Why is the last 'append('apple')' code not output normally in the 'Group_of_append' function?
...ANSWER
Answered 2022-Mar-28 at 12:28Your appends work fine. Problem lies in your print_list function which stops when p.next is None. Which means your last element will not be printed because its next is None.
All in all, your logic for this list is very strange and could use a lot of rework, it would make finding mistakes like this one a lot easier for you. For example, this iterating through the whole list when appending even though you have both head and tail readily available in the deque object.
QUESTION
auto queue = [](string str) {
istringstream ss(str);
//std::copy(std::istream_iterator(ss),
// std::istream_iterator(),
// std::ostream_iterator(std::cout, " "));
//deque q(std::istream_iterator(ss), std::istream_iterator{});
deque q(std::istream_iterator(ss), std::istream_iterator());
return q;
};
ANSWER
Answered 2022-Mar-28 at 12:23This line
QUESTION
As I understand, any container that supports push_back(), pop_back() and back() can be used as the underlying container for stacks, but by default, deques are used. I understand the pros of deques over vectors generally (possibility to add elements at the beginning as well as at the end), but in the case of stacks, I don't see any reason to prefer deques.
...ANSWER
Answered 2022-Mar-16 at 15:52I don't see any reason to prefer deques.
A reason to prefer deque that applies to the stack use case is that individual push back has worst case constant complexity compared to vector whose individual push back is linear in worst case (it has amortised constant complexity over multiple push backs). This was particularly significant prior to C++11 when reallocating vector had to copy the elements which could be very expensive. Consider case where the elements themselves are long strings.
Another reason to prefer deques is that they release memory as they shrink. Vectors don't. Hence, if you have a stack that temporarily grows large, then shrinks and remains small for the rest of the execution, then an underlying vector would be wasting a lot of memory.
Historically, when STL was designed and thus when the default was chosen, there used to also be issues with very large vectors because the size of the address space didn't exceed (significantly, or at all) the amount of memory (this was before 64 bit processing was common). The consequence of the limited address space was that memory fragmentation would make it expensive or impossible to allocate large contiguous blocks of memory that a large vector would require. Furthermore, the way that vector grows by deallocating old buffers is a behaviour that causes such fragmentation.
QUESTION
I am using this code for searching a target_string in a single input file (input.txt) and "extracting" those lines with the target_string in an output file (output.txt). Now I want to perform the same procedure but with several input files, for instance, input1.txt, input2.txt, input3.txt, ...
How can I modify this code for doing this?
...ANSWER
Answered 2022-Mar-04 at 16:45For example:
QUESTION
I'm trying to build a Golang project, which contains different levels of packages inside. I've uploaded an example project here: https://github.com/David-Lor/archive.org-telegrambot/tree/example-go-dockerfile-not-building
Filesgo.mod
...ANSWER
Answered 2022-Feb-16 at 23:06The issue is in your Dockerfile; after the operation COPY ./src/* ./ the directory structure in your image is as follows:
QUESTION
Hello there I'm facing some issues with the navigation between fragments
ok I explain in detail
I have a bottom nav with 4 fragments Home, Following, Notification, and Profile, there is no issue with the bottom navigation on backstack , but now for eg from profile fragment I jumped to a fragment called edit_profile which is not a part of the bottom nav and when press back I want that it should go back to the profile fragment but the backstack is taking me from edit_profile to directly home fragment
here is a recording link
I recently change my project from java to kotlin and I'm a beginner in kotlin
i really like the navigation of Pinterest and Instagram
Note:- All this code is automatically changed to kotlin (with some changes done manually ) , this issue was also with java and not after migrating to kotlin , Also if you want more reference of the code please tell me i will update the question
Code
MainActivity.kt // Bottom Nav
...ANSWER
Answered 2022-Jan-13 at 10:08Where I add HomeF in main container which includes all bottom nav tab, and all bottom nav tab will open in home container, and those fragment which are not part of bottom nav will open in main container. I generally add(not replace) all the fragments in main container and set add to back stack , so that if user goes from profile (home_container) to something in main container , while backstack we can pop the top fragment and user will be seeing profile.
QUESTION
I am making a scrolling graph which will plot real-time sensor data, with time on the x axis. I am a bit confused by the behavior of tickStrings.
My code is based on the example below (from here). As the number of points plotted increases, the number of x axis strings varies - sometimes it increases and sometimes it decreases . It stabilizes once the deque is full length and the 'scrolling' begins.
Is it possible to keep the spacing between tick strings the same as the number of plotted points increases? I guess that it might be possible use an approach where blank tick strings are replaced as new data is added, but don't know how to do that.
Edit: An example of what I wish to achieve is here.
...ANSWER
Answered 2022-Feb-02 at 13:32To set constant number of ticks, You have to override tickValues method as well. This method generates tick values and tickStrings method gives these values string representation - conversion to human readable time in Your case.
Here is example of TimeAxisItem You can use in Your code:
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