在比较 std::vector 和 std::deque 的效率时，必须考虑它们在不同情况下的性能特点。
虽然 deque 的扩展(增加空间的大小)通常比vector的扩展开销更小，因为它不需要将现有元素复制到新的内存中，但效率会因执行的具体操作而不同。
就插入而言，deque 通常被认为比vector更高效。在随机位置或前端插入元素时尤其如此，因为 deque 可以在两端提供恒定时间插入。另一方面，如果在中间插入新元素，vector可能需要对元素进行移位，从而可能导致性能降低。
不过，值得注意的是，在随机访问元素时，vector的效率可能更高，因为vector将元素存储在连续的内存块中。与将元素存储在多个内存块中的 deque 相比，这可以带来更好的缓存性能和更快的访问速度。
vector在末尾插入元素时的摊销时间复杂度为常量 O(1)，但在容器开头或中间插入元素时的线性时间复杂度为 O(n)（因为所有后续元素都需要移位）。而 Deques 在前后插入时的时间复杂度都是恒定的 O(1)，因此在需要频繁插入或删除头部元素的情况下更有效。
就性能而言，vector由于其连续的内存布局，在随机存取和顺序遍历方面通常优于deques。不过，在需要在容器前端或后端频繁插入或删除元素的情况下，deques 的性能可能会优于vector。
总之，虽然 deque 在随机位置或前端插入的效率可能比 vector 高，但 vector 由于其连续的内存布局，在随机存取方面可能提供更好的性能。在vector和 deque 之间做出选择时，应根据应用程序的具体要求和正在执行的操作而定。
如果你主要需要高效的随机访问和顺序遍历，vectors是一个不错的选择。另一方面，如果需要在容器的前端或后端进行高效的插入或删除操作，deques 可以提供更好的性能。
When comparing the efficiency of std::vector and std::deque, it is important to consider their performance characteristics in different scenarios.
While expansion of a deque is generally cheaper than expanding a vector because it doesn't involve copying existing elements to new memory, the efficiency can vary depending on the specific operation being performed.
In terms of insertion, deque is generally considered to be more efficient than vector. This is especially true when inserting elements at random positions or at the front, as deque provides constant-time insertion at both ends. On the other hand, vector may require elements to be shifted if new elements are inserted in the middle, resulting in potentially slower performance.
However, it's important to note that the efficiency of vector may be better when it comes to accessing elements randomly, as vector stores its elements in a contiguous block of memory. This can lead to better cache performance and faster access compared to deque, which stores its elements in multiple blocks of memory.
Vectors have a constant amortized time complexity O(1) for inserting elements at the end, but have a linear time complexity O(n) for inserting elements at the beginning or middle of the container (since all subsequent elements need to be shifted). Deques, however, have a constant time complexity O(1) for both front and back insertion, making them more efficient in scenarios where frequent insertion or deletion at the front is required.
In terms of performance, vectors generally outperform deques when it comes to random access and sequential traversal due to their contiguous memory layout. However, deques may perform better than vectors in situations where frequent insertion or deletion is required at the front or back of the container.
In summary, while deque may be more efficient than vector in terms of insertion at random positions or at the front, vector may offer better performance for random access due to its contiguous memory layout. The choice between vector and deque should be based on the specific requirements of the application and the operations being performed.
If you primarily need efficient random access and sequential traversal, vectors are a good choice. On the other hand, if you require efficient insertion or deletion at the front or back of the container, deques offer better performance.
参考：
1，LINER AI
免费版， GPT-3.5：vector vs deque