std::ranges::partial_sort
Defined in header <algorithm> |
||
|---|---|---|
| Call signature | ||
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
partial_sort( I first, I middle, S last, Comp comp = {}, Proj proj = {} ); |
(1) | (since C++20) |
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>
partial_sort( R&& r, ranges::iterator_t<R> middle, Comp comp = {},
Proj proj = {} ); |
(2) | (since C++20) |
1) Rearranges elements such that the range
[first, middle) contains the sorted
middle - first smallest elements in the range
[first, last).
The order of equal elements is
not guaranteed to be preserved. The order of the remaining elements in the range
[middle, last) is
unspecified.
The elements are compared using the given binary comparison function
comp and projected using
proj function object.
2) Same as
(1), but uses
r as the range, as if using
ranges::begin(r) as
first and
ranges::end(r) as
last.
The function-like entities described on this page are niebloids, that is:
- Explicit template argument lists may not be specified when calling any of them.
- None of them is visible to argument-dependent lookup.
- When one of them is found by normal unqualified lookup for the name to the left of the function-call operator, it inhibits argument-dependent lookup.
In practice, they may be implemented as function objects, or with special compiler extensions.
Parameters
| first, last | - | iterator-sentinel defining the range to sort |
| r | - | the range to sort |
| middle | - | the iterator defining the last element to be sorted |
| comp | - | comparator to apply to the projected elements |
| proj | - | projection to apply to the elements |
Return value
An iterator equal to last.
Complexity
\(\scriptsize \mathcal{O}(N\cdot\log{(M)})\)𝓞(N·log(M)) comparisons and twice as many projections, where \(\scriptsize N\)N is ranges::distance(first, last), \(\scriptsize M\)M is ranges::distance(first, middle).
Possible implementation
struct partial_sort_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, I middle, S last, Comp comp = {}, Proj proj = {} ) const {
if (first == middle) return ranges::next(first, last);
ranges::make_heap(first, middle, comp, proj);
auto it {middle};
for (; it != last; ++it) {
if (std::invoke(comp, std::invoke(proj, *it), std::invoke(proj, *first))) {
ranges::pop_heap(first, middle, comp, proj);
ranges::iter_swap(middle - 1, it);
ranges::push_heap(first, middle, comp, proj);
}
}
ranges::sort_heap(first, middle, comp, proj);
return it;
}
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, ranges::iterator_t<R> middle, Comp comp = {}, Proj proj = {} ) const {
return (*this)(ranges::begin(r), std::move(middle), ranges::end(r),
std::move(comp), std::move(proj));
}
};
inline constexpr partial_sort_fn partial_sort{};
|
Example
#include <algorithm>
#include <functional>
#include <iostream>
#include <string>
#include <vector>
void print(const auto& v) {
for (const char e : v) { std::cout << e << ' '; }
std::cout << '\n';
}
void underscore(int n) {
while (n-- > 0) { std::cout << "^ "; }
std::cout << '\n';
}
int main()
{
static_assert('A' < 'a');
std::vector<char> v{'x', 'P', 'y', 'C', 'z', 'w', 'P', 'o'};
print(v);
std::ranges::partial_sort(v, v.begin() + 3);
print(v); underscore(3);
static_assert('1' < 'a');
std::string s{"3a1b41c5"};
print(s);
std::ranges::partial_sort(s.begin(), s.begin() + 3, s.end(), std::greater{});
print(s); underscore(3);
}
Output:
x P y C z w P o C P P y z x w o ^ ^ ^ 3 a 1 b 4 1 c 5 c b a 1 3 1 4 5 ^ ^ ^
See also
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(C++20)
|
copies and partially sorts a range of elements (niebloid) |
|
(C++20)
|
sorts a range into ascending order (niebloid) |
|
(C++20)
|
sorts a range of elements while preserving order between equal elements (niebloid) |
|
(C++20)
|
partially sorts the given range making sure that it is partitioned by the given element (niebloid) |
|
(C++20)
|
creates a max heap out of a range of elements (niebloid) |
|
(C++20)
|
removes the largest element from a max heap (niebloid) |
|
(C++20)
|
adds an element to a max heap (niebloid) |
|
(C++20)
|
turns a max heap into a range of elements sorted in ascending order (niebloid) |
| sorts the first N elements of a range (function template) |
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