std::ranges::sort_heap() algorithm
- od C++20
- Simplified
- Detailed
// (1)
constexpr I
sort_heap( I first, S last, Comp comp = {}, Proj proj = {} );
// (2)
constexpr ranges::borrowed_iterator_t<R>
sort_heap( R&& r, Comp comp = {}, Proj proj = {} );
The type of arguments are generic and have the following constraints:
I
-std::random_access_iterator
S
-std::sentinel_for<I>
R
-std::ranges::random_access_range
Comp
- (none)Proj
- (none)
The Proj
and Comp
template arguments have the following default types: std::identity
, ranges::less
for all overloads.
Additionally, each overload has the following constraints:
- (1) -
std::sortable<I, Comp, Proj>
- (2) -
std::sortable<ranges::iterator_t<R>, Comp, Proj>
// (1)
template<
std::random_access_iterator I,
std::sentinel_for<I> S,
class Comp = ranges::less,
class Proj = std::identity
>
requires std::sortable<I, Comp, Proj>
constexpr I
sort_heap( I first, S last, Comp comp = {}, Proj proj = {} );
// (2)
template<
ranges::random_access_range R,
class Comp = ranges::less,
class Proj = std::identity
>
requires std::sortable<ranges::iterator_t<R>, Comp, Proj>
constexpr ranges::borrowed_iterator_t<R>
sort_heap( R&& r, Comp comp = {}, Proj proj = {} );
Converts the max heap [first
; last
) into a sorted range in ascending order.
The resulting range no longer has the heap property.
-
(1) Elements are compared using the given binary comparison function
comp
and projection objectproj
. -
(2) Same as (1), but uses
r
as the source range, as if usingranges::begin(r)
asfirst
andranges::end(r)
aslast
.
The function-like entities described on this page are niebloids.
Parameters
first last | The range of elements to make a heap from. |
r | The range of elements to make a heap from. |
pred | Predicate to apply to the projected elements. |
proj | The projection to apply to the elements. |
Return value
An iterator equal to last
.
Complexity
Given N
as ranges::distance(first, last)
:
At most 2 * N * log(N) comparisons and 4 * N * log(N) projections.
Exceptions
(none)
Possible implementation
sort_heap(1) and sort_heap(2)
struct sort_heap_fn
{
template<std::random_access_iterator I, std::sentinel_for<I> S,
class Comp = ranges::less, class Proj = std::identity>
requires std::sortable<I, Comp, Proj>
constexpr I
operator()(I first, S last, Comp comp = {}, Proj proj = {}) const
{
auto ret {ranges::next(first, last)};
for (; first != last; --last)
ranges::pop_heap(first, last, comp, proj);
return ret;
}
template<ranges::random_access_range R, class Comp = ranges::less,
class Proj = std::identity>
requires std::sortable<ranges::iterator_t<R>, Comp, Proj>
constexpr ranges::borrowed_iterator_t<R>
operator()(R&& r, Comp comp = {}, Proj proj = {}) const
{
return (*this)(ranges::begin(r), ranges::end(r), std::move(comp), std::move(proj));
}
};
inline constexpr sort_heap_fn sort_heap {};
Notes
A max heap is a range of elements [f
; l
), arranged with respect to comparator comp
and projection proj
, that has the following properties:
- Given
N
asl - f
,p = f[(i - 1) / 2]
, andq = f[i]
, for all0 < i < N
, the expressionstd::invoke(comp, std::invoke(proj, p), std::invoke(proj, q))
evaluates tofalse
. - A new element can be added using
ranges::push_heap
, in O(log(N)) time. - The first element can be removed using
ranges::pop_heap
, in O(log(N)) time.
Examples
#include <algorithm>
#include <array>
#include <iostream>
void print(auto const& rem, auto const& v)
{
std::cout << rem;
for (const auto i : v)
std::cout << i << ' ';
std::cout << '\n';
}
int main()
{
std::array v {3, 1, 4, 1, 5, 9};
print("original array: ", v);
std::ranges::make_heap(v);
print("after make_heap: ", v);
std::ranges::sort_heap(v);
print("after sort_heap: ", v);
}
original array: 3 1 4 1 5 9
after make_heap: 9 5 4 1 1 3
after sort_heap: 1 1 3 4 5 9
Hover to see the original license.