std::sort_heap - cppreference.com (original) (raw)

Defined in header
template< class RandomIt > void sort_heap( RandomIt first, RandomIt last ); (1) (constexpr since C++20)
template< class RandomIt, class Compare > void sort_heap( RandomIt first, RandomIt last, Compare comp ); (2) (constexpr since C++20)

Converts the heap [first, last) into a sorted range. The heap property is no longer maintained.

  1. The heap is with respect to operator<(until C++20)std::less{}(since C++20), and will be sorted with respect to operator<(until C++20)std::less{}(since C++20).

  2. The heap is with respect to comp, and will be sorted with respect to comp.

If any of the following conditions is satisfied, the behavior is undefined:

Contents

[edit] Parameters

first, last - the pair of iterators defining the binary heap range of elements to make the sorted range
comp - comparison function object (i.e. an object that satisfies the requirements of Compare) which returns true if the first argument is less than the second.The signature of the comparison function should be equivalent to the following:bool cmp(const Type1& a, const Type2& b); While the signature does not need to have const&, the function must not modify the objects passed to it and must be able to accept all values of type (possibly const) Type1 and Type2 regardless of value category (thus, Type1& is not allowed, nor is Type1 unless for Type1 a move is equivalent to a copy(since C++11)).The types Type1 and Type2 must be such that an object of type RandomIt can be dereferenced and then implicitly converted to both of them.
Type requirements
-RandomIt must meet the requirements of LegacyRandomAccessIterator.
-Compare must meet the requirements of Compare.

[edit] Complexity

Given \(\scriptsize N\)N as std::distance(first, last):

  1. At most \(\scriptsize 2N \cdot \log(N)\)2N⋅log(N) comparisons using operator<(until C++20)std::less{}(since C++20).

  2. At most \(\scriptsize 2N \cdot \log(N)\)2N⋅log(N) applications of the comparison function comp.

[edit] Possible implementation

sort_heap (1)
template<class RandomIt> void sort_heap(RandomIt first, RandomIt last) { while (first != last) std::pop_heap(first, last--); }
sort_heap (2)
template<class RandomIt, class Compare> void sort_heap(RandomIt first, RandomIt last, Compare comp) { while (first != last) std::pop_heap(first, last--, comp); }

[edit] Example

#include #include #include #include   void println(std::string_view fmt, const auto& v) { for (std::cout << fmt; const auto &i : v) std::cout << i << ' '; std::cout << '\n'; }   int main() { std::vector v{3, 1, 4, 1, 5, 9};   std::make_heap(v.begin(), v.end()); println("after make_heap, v: ", v);   std::sort_heap(v.begin(), v.end()); println("after sort_heap, v: ", v); }

Output:

after make_heap, v: 9 4 5 1 1 3 after sort_heap, v: 1 1 3 4 5 9

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 2444 C++98 at most \(\scriptsize N \cdot \log(N)\)N⋅log(N) comparisons were allowed increased to \(\scriptsize 2N \cdot \log(N)\)2N⋅log(N)

[edit] See also

is_heap(C++11) checks if the given range is a max heap (function template) [edit]
is_heap_until(C++11) finds the largest subrange that is a max heap (function template) [edit]
make_heap creates a max heap out of a range of elements (function template) [edit]
pop_heap removes the largest element from a max heap (function template) [edit]
push_heap adds an element to a max heap (function template) [edit]
ranges::sort_heap(C++20) turns a max heap into a range of elements sorted in ascending order(algorithm function object)[edit]