deque

问题 This wiki.python.org page on algorithmic complexity of some data structures says the following for a collections.deque object: A deque (double-ended queue) is represented internally as a doubly linked list. (Well, a list of arrays rather than objects, for greater efficiency.) Both ends are accessible, but even looking at the middle is slow, and adding to or removing from the middle is slower still. Two questions: 1) Is adding to the middle of a deque even possible? I don't see any method to

问题 This wiki.python.org page on algorithmic complexity of some data structures says the following for a collections.deque object: A deque (double-ended queue) is represented internally as a doubly linked list. (Well, a list of arrays rather than objects, for greater efficiency.) Both ends are accessible, but even looking at the middle is slow, and adding to or removing from the middle is slower still. Two questions: 1) Is adding to the middle of a deque even possible? I don't see any method to

问题 I read here from the accepted answer that a std::deque has the following characteristic 1- Random access - constant O(1) 2- Insertion or removal of elements at the end or beginning - amortized constant O(1) 3- Insertion or removal of elements - linear O(n) My question is about point 2. How can a deque have an amortized constant insertion at the end or beginning? I understand that a std::vector has an amortized constant time complexity for insertions at the end. This is because a vector is

问题 I am trying to put the frames of a video in a deque. This code does not work. Because the back and front of the queue are both the same as the current frame. deque<Mat> frameSeq; int main() { Mat frame; VideoCapture video("path to video"); int key = 0; while (key != 'q') { video >> frame; frameSeq.push_back(frame); imshow("front", frameSeq.front()); imshow("back", frameSeq.back()); key = cvWaitKey(1); } return 0; } But when I resize the frame: deque<Mat> frameSeq; int main() { Mat frame;

问题 This is my code: import java.util.ArrayDeque; import java.util.Collections; import java.util.Deque; import java.util.List; public class ArrayDequeDemo { public static void main(String[] args) { // create an empty array deque with an initial capacity Deque<Integer> deque = new ArrayDeque<Integer>(8); // use add() method to add elements in the deque deque.add(15); deque.add(30); deque.add(20); deque.add(18); // let us print all the elements available in deque for (Integer number : deque) {

问题 This question already has answers here : Why would I prefer using vector to deque (10 answers) Closed 18 days ago . As vector and deque both provides a function to push_back the element at the last. where deque also provides a function push_front to insert the element at the beginning, which is bit costly in case of vector . My question is when we can achieve the same functionality ( push_back ) of vector by using deque , then why vector is required? 回答1: One main difference between vectors

问题 Exist a faster way to merge two deques than this? # a, b are two deques. The maximum length # of a is greater than the current length # of a plus the current length of b while len(b): a.append(b.popleft()) Note that I'm not interested in preserving input deques, I'm only interested in having the merged one as fast as possible. 回答1: There's no need for elementwise appending, you can just use += : from collections import deque a = deque([1, 2, 3]) b = deque([4, 5, 6]) a += b print(a) deque([1,

问题 I understand that both deque and vector reserve some space for growth. vector::capacity() is able to get the internal reserved space for a vector. Deque doesn't have such a member in the standard. Is there some way to get this information? 回答1: You'd have to dig into the implementation to figure that out. The version of std::deque that comes with gcc 4.1.1 appears to allocate memory in 512 byte chunks. But that's as far as I got after 15 minutes of staring at all the underscores and C-style

问题 I understand that both deque and vector reserve some space for growth. vector::capacity() is able to get the internal reserved space for a vector. Deque doesn't have such a member in the standard. Is there some way to get this information? 回答1: You'd have to dig into the implementation to figure that out. The version of std::deque that comes with gcc 4.1.1 appears to allocate memory in 512 byte chunks. But that's as far as I got after 15 minutes of staring at all the underscores and C-style

问题 I was working on a problem on LeetCode (Here). When I finished the problem, I came up with: class MovingAverage { std::deque<int> numsToAverage; int maxSize; int currentTotal; public: /** Initialize your data structure here. */ MovingAverage(int size) { maxSize = size; currentTotal = 0; } double next(int val) { currentTotal += val; numsToAverage.push_back(val); if (numsToAverage.size() > maxSize) { currentTotal -= numsToAverage[0]; numsToAverage.pop_front(); } return (double)currentTotal /