std::ranges::partial_sort
From cppreference.com
| Defined in header <algorithm>
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| Call signature |
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| template< std::random_access_iterator I, std::sentinel_for<I> S, class Comp = ranges::less, class Proj = std::identity > |
(1) | (since C++20) |
| template< ranges::random_access_range R, class Comp = ranges::less, class Proj = std::identity > |
(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 cannot be specified when calling any of them.
- None of them are visible to argument-dependent lookup.
- When any of them are found by normal unqualified lookup as the name to the left of the function-call operator, argument-dependent lookup is inhibited.
In practice, they may be implemented as function objects, or with special compiler extensions.
Contents |
[edit] 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 |
[edit] Return value
An iterator equal to last.
[edit] Complexity
𝓞(N·log(M)) comparisons and twice as many projections, where N is ranges::distance(first, last), M is ranges::distance(first, middle).
[edit] 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 {}; |
[edit] Example
Run this code
#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); const int m {3}; std::ranges::partial_sort(v, v.begin() + m); print(v), underscore(m); static_assert('1' < 'a'); std::string s {"3a1b41c5"}; print(s); std::ranges::partial_sort(s.begin(), s.begin() + m, s.end(), std::greater {}); print(s), underscore(m); }
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 ^ ^ ^
[edit] See also
| (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) |
