std::ranges::is_sorted_until
| Defined in header <algorithm>
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| Call signature |
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| template< std::forward_iterator I, std::sentinel_for<I> S, class Proj = std::identity, std::indirect_strict_weak_order<std::projected<I, Proj>> Comp = ranges::less > |
(1) | (since C++20) |
| template< std::forward_range R, class Proj = std::identity, std::indirect_strict_weak_order< |
(2) | (since C++20) |
Examines the range [first, last) and finds the largest range beginning at first in which the elements are sorted in non-descending order.
A sequence is sorted with respect to a comparator comp if for any iterator it pointing to the sequence and any non-negative integer n such that it + n is a valid iterator pointing to an element of the sequence, std::invoke(comp, std::invoke(proj, *(it + n)), std::invoke(proj, *it)) evaluates to false.
comp.r as the source 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 find its sorted upper bound |
| r | - | the range to find its sorted upper bound |
| comp | - | comparison function to apply to the projected elements |
| proj | - | projection to apply to the elements |
Return value
The upper bound of the largest range beginning at first in which the elements are sorted in non-descending order. That is, the last iterator it for which range [first, it) is sorted.
Complexity
Linear in the distance between first and last.
Possible implementation
struct is_sorted_until_fn { template<std::forward_iterator I, std::sentinel_for<I> S, class Proj = std::identity, std::indirect_strict_weak_order<std::projected<I, Proj>> Comp = ranges::less> constexpr I operator()(I first, S last, Comp comp = {}, Proj proj = {}) const { if (first == last) { return first; } auto next = first; while (++next != last) { if (std::invoke(comp, std::invoke(proj, *next), std::invoke(proj, *first))) { return next; } first = next; } return first; } template< ranges::forward_range R, class Proj = std::identity, std::indirect_strict_weak_order< std::projected<ranges::iterator_t<R>, Proj>> Comp = ranges::less > constexpr ranges::borrowed_iterator_t<R> operator()( R&& r, Comp comp = {}, Proj proj = {} ) const { return (*this)(ranges::begin(r), ranges::end(r), std::ref(comp), std::ref(proj)); } }; inline constexpr is_sorted_until_fn is_sorted_until; |
Notes
ranges::is_sorted_until returns an iterator equal to last for empty ranges and ranges of length one.
Example
#include <algorithm> #include <iostream> #include <iterator> #include <random> int main() { std::random_device rd; std::mt19937 g{rd()}; std::array nums {3, 1, 4, 1, 5, 9}; constexpr int min_sorted_size = 4; int sorted_size = 0; do { std::ranges::shuffle(nums, g); const auto sorted_end = std::ranges::is_sorted_until(nums); sorted_size = std::ranges::distance(nums.begin(), sorted_end); std::ranges::copy(nums, std::ostream_iterator<int>(std::cout, " ")); std::cout << " : " << sorted_size << " leading sorted element(s)\n"; } while (sorted_size < min_sorted_size); }
Possible output:
4 1 9 5 1 3 : 1 leading sorted element(s) 4 5 9 3 1 1 : 3 leading sorted element(s) 9 3 1 4 5 1 : 1 leading sorted element(s) 1 3 5 4 1 9 : 3 leading sorted element(s) 5 9 1 1 3 4 : 2 leading sorted element(s) 4 9 1 5 1 3 : 2 leading sorted element(s) 1 1 4 9 5 3 : 4 leading sorted element(s)
See also
| (C++20) |
checks whether a range is sorted into ascending order (niebloid) |
| (C++11) |
finds the largest sorted subrange (function template) |