在 C++ STL 中使用 priority_queue 和 vector 创建堆的时间复杂度是多少？

Question

We have been taught that time complexity for building a min or max heap from scratch takes O(n) time.

But since priority_queue in STL takes O(log n) time for insertion,

So making heap from scratch using priority_queue would take O(n*log n) time. isn't it? and same goes for using vector also. Is there any other way in which I could use any built-in function from STL to create heap in O(n) time?

Answer 1

std::priority_queue 's constructors all have O(N) complexity ¹ , where N is the number of elements you pass.

Eg

explicit priority_queue( const Compare& compare = Compare(), const Container& cont = Container() ); (3)

3. Copy-constructs the underlying container c with the contents of cont . Copy-constructs the comparison functor comp with the contents of compare . Calls std::make_heap(c.begin(), c.end(), comp) .

Complexity

3. O(N) comparisons, where N is cont.size() . Additionally, O(N) calls to the constructor of value_type , where N is cont.size() .

1. Besides the move constructor, which steals it's argument in constant time.