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std::ranges::rotate(3) C++ Standard Libary std::ranges::rotate(3) NAME std::ranges::rotate - std::ranges::rotate Synopsis Defined in header <algorithm> Call signature template< std::permutable I, std::sentinel_for<I> S > constexpr ranges::subrange<I> (1) (since C++20) rotate( I first, I middle, S last ); template< ranges::forward_range R > requires std::permutable<ranges::iterator_t<R>> (2) (since C++20) constexpr ranges::borrowed_subrange_t<R> rotate( R&& r, ranges::iterator_t<R> middle ); 1) Performs a left rotation on a range of elements. Specifically, ranges::rotate swaps the elements in the range [first, last) in such a way that the element *middle becomes the first element of the new range and *(middle - 1) becomes the last element. The behavior is undefined if [first, last) is not a valid range or middle is not in [first, last). 2) Same as (1), but uses r as the range, as if using ranges::be- gin(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 call- ing 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 in- hibited. In practice, they may be implemented as function objects, or with special compiler extensions. Parameters first, last - the range of elements to rotate r - the range of elements to rotate middle - the iterator to the element that should appear at the beginning of the rotated range Return value {new_first, last}, where new_first compares equal to ranges::next(first, ranges::distance(middle, last)) and designates a new location of the element pointed by first. Complexity Linear at worst: ranges::distance(first, last) swaps. Notes ranges::rotate has better efficiency on common implementations if I models bidirectional_iterator or (better) random_access_iterator. Implementations (e.g. MSVC STL) may enable vectorization when the iterator type models contiguous_iterator and swapping its value type calls neither non-trivial special member function nor ADL-found swap. Possible implementation See also the implementations in libstdc++ and MSVC STL. struct rotate_fn { template<std::permutable I, std::sentinel_for<I> S> constexpr ranges::subrange<I> operator()(I first, I middle, S last) const { if (first == middle) { auto last_it = ranges::next(first, last); return {last_it, last_it}; } if (middle == last) return {std::move(first), std::move(middle)}; if constexpr (std::bidirectional_iterator<I>) { ranges::reverse(first, middle); auto last_it = ranges::next(first, last); ranges::reverse(middle, last_it); if constexpr (std::random_access_iterator<I>) { ranges::reverse(first, last_it); return {first + (last_it - middle), std::move(last_it)}; } else { auto mid_last = last_it; do { ranges::iter_swap(first, --mid_last); ++first; } while (first != middle && mid_last != middle); ranges::reverse(first, mid_last); if (first == middle) return {std::move(mid_last), std::move(last_it)}; else return {std::move(first), std::move(last_it)}; } } else { // I is merely a forward_iterator auto next_it = middle; do { // rotate the first cycle ranges::iter_swap(first, next_it); ++first; ++next_it; if (first == middle) middle = next_it; } while (next_it != last); auto new_first = first; while (middle != last) { // rotate subsequent cycles next_it = middle; do { ranges::iter_swap(first, next_it); ++first; ++next_it; if (first == middle) middle = next_it; } while (next_it != last); } return {std::move(new_first), std::move(middle)}; } } template<ranges::forward_range R> requires std::permutable<ranges::iterator_t<R>> constexpr ranges::borrowed_subrange_t<R> operator()(R&& r, ranges::iterator_t<R> middle) const { return (*this)(ranges::begin(r), std::move(middle), ranges::end(r)); } }; inline constexpr rotate_fn rotate {}; Example ranges::rotate is a common building block in many algorithms. This example demonstrates insertion sort. // Run this code #include <algorithm> #include <iostream> #include <numeric> #include <string> #include <vector> int main() { std::string s(16, ' '); for (int k {}; k != 5; ++k) { std::iota(s.begin(), s.end(), 'A'); std::ranges::rotate(s, s.begin() + k); std::cout << "Rotate left (" << k << "): " << s << '\n'; } std::cout << '\n'; for (int k {}; k != 5; ++k) { std::iota(s.begin(), s.end(), 'A'); std::ranges::rotate(s, s.end() - k); std::cout << "Rotate right (" << k << "): " << s << '\n'; } std::cout << "\nInsertion sort using `rotate`, step-by-step:\n"; s = {'2', '4', '2', '0', '5', '9', '7', '3', '7', '1'}; for (auto i = s.begin(); i != s.end(); ++i) { std::cout << "i = " << std::ranges::distance(s.begin(), i) << ": "; std::ranges::rotate(std::ranges::upper_bound(s.begin(), i, *i), i, i + 1); std::cout << s << '\n'; } std::cout << (std::ranges::is_sorted(s) ? "Sorted!" : "Not sorted.") << '\n'; } Output: Rotate left (0): ABCDEFGHIJKLMNOP Rotate left (1): BCDEFGHIJKLMNOPA Rotate left (2): CDEFGHIJKLMNOPAB Rotate left (3): DEFGHIJKLMNOPABC Rotate left (4): EFGHIJKLMNOPABCD Rotate right (0): ABCDEFGHIJKLMNOP Rotate right (1): PABCDEFGHIJKLMNO Rotate right (2): OPABCDEFGHIJKLMN Rotate right (3): NOPABCDEFGHIJKLM Rotate right (4): MNOPABCDEFGHIJKL Insertion sort using `rotate`, step-by-step: i = 0: 2420597371 i = 1: 2420597371 i = 2: 2240597371 i = 3: 0224597371 i = 4: 0224597371 i = 5: 0224597371 i = 6: 0224579371 i = 7: 0223457971 i = 8: 0223457791 i = 9: 0122345779 Sorted! See also ranges::rotate_copy copies and rotate a range of elements (C++20) (niebloid) ranges::reverse reverses the order of elements in a range (C++20) (niebloid) rotate rotates the order of elements in a range (function template) http://cppreference.com 2024.06.10 std::ranges::rotate(3)
NAME | Synopsis | Parameters | Return value | Complexity | Notes | Possible implementation | Example | Output: | See also
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