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std::ranges::is_heap_until(3) C++ Standard Libarystd::ranges::is_heap_until(3) NAME std::ranges::is_heap_until - std::ranges::is_heap_until Synopsis Defined in header <algorithm> Call signature template< std::random_access_iterator I, std::sentinel_for<I> S, class Proj = std::identity, std::indirect_strict_weak_or- der< (since std::projected<I, Proj>> Comp = ranges::less > (1) C++20) constexpr I is_heap_until( I first, S last, Comp comp = {}, Proj proj = {} ); template< ranges::random_access_range R, class Proj = std::identity, std::indirect_strict_weak_order<std::projected<ranges::itera- tor_t<R>, (since Proj>> (2) C++20) Comp = ranges::less > constexpr ranges::borrowed_iterator_t<R> is_heap_until( R&& r, Comp comp = {}, Proj proj = {} ); Examines the range [first, last) and finds the largest range begin- ning at first which is a max heap. 1) Elements are compared using the given binary comparison function comp and projection object proj. 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 examine r - the range of elements to examine pred - predicate 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 which is a max heap. That is, the last iterator it for which range [first, it) is a max heap with respect to comp and proj. Complexity Linear in the distance between first and last. 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: * With N = l - f, p = f[(i - 1) / 2], and q = f[i], for all 0 < i < N, the expression std::invoke(comp, std::invoke(proj, p), std::in- voke(proj, q)) evaluates to false. * A new element can be added using ranges::push_heap, in \(\scriptsize \mathcal{O}(\log N)\)(log N) time. * The first element can be removed using ranges::pop_heap, in \(\scriptsize \mathcal{O}(\log N)\)(log N) time. Possible implementation struct is_heap_until_fn { template<std::random_access_iterator I, std::sentinel_for<I> S, class Proj = std::identity, std::indirect_strict_weak_or- der< std::projected<I, Proj>> Comp = ranges::less> constexpr I operator()(I first, S last, Comp comp = {}, Proj proj = {}) const { std::iter_difference_t<I> n{ranges::distance(first, last)}, dad{0}, son{1}; for (; son != n; ++son) { if (std::invoke(comp, std::invoke(proj, *(first + dad)), std::invoke(proj, *(first + son)))) return first + son; else if ((son % 2) == 0) ++dad; } return first + n; } template<ranges::random_access_range R, class Proj = std::identity, std::indirect_strict_weak_order<std::projected<ranges::it- erator_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::move(comp), std::move(proj)); } }; inline constexpr is_heap_until_fn is_heap_until {}; Example The example renders a given vector as a (balanced) Binary tree. // Run this code #include <algorithm> #include <cmath> #include <iostream> #include <iterator> #include <vector> void out(const auto& what, int n = 1) { while (n-- > 0) std::cout << what; } void draw_bin_tree(auto first, auto last) { auto bails = [](int n, int w) { auto b = [](int w) { out(""), out("", w), out(""), out("", w), out(""); }; n /= 2; if (!n) return; for (out(' ', w); n-- > 0;) b(w), out(' ', w + w + 1); out('\n'); }; auto data = [](int n, int w, auto& first, auto last) { for (out(' ', w); n-- > 0 && first != last; ++first) out(*first), out(' ', w + w + 1); out('\n'); }; auto tier = [&](int t, int m, auto& first, auto last) { const int n{1 << t}; const int w{(1 << (m - t - 1)) - 1}; bails(n, w), data(n, w, first, last); }; const auto size{std::ranges::distance(first, last)}; const int m{static_cast<int>(std::ceil(std::log2(1 + size)))}; for (int i{}; i != m; ++i) tier(i, m, first, last); } int main() { std::vector<int> v{3, 1, 4, 1, 5, 9}; std::ranges::make_heap(v); // probably mess up the heap v.push_back(2); v.push_back(6); out("v after make_heap and push_back:\n"); draw_bin_tree(v.begin(), v.end()); out("the max-heap prefix of v:\n"); const auto heap_end = std::ranges::is_heap_until(v); draw_bin_tree(v.begin(), heap_end); } Output: v after make_heap and push_back: 9 5 4 1 1 3 2 6 the max-heap prefix of v: 9 5 4 1 1 3 2 See also ranges::is_heap checks if the given range is a max heap (C++20) (niebloid) ranges::make_heap creates a max heap out of a range of elements (C++20) (niebloid) ranges::push_heap adds an element to a max heap (C++20) (niebloid) ranges::pop_heap removes the largest element from a max heap (C++20) (niebloid) ranges::sort_heap turns a max heap into a range of elements sorted in ascending (C++20) order (niebloid) is_heap_until finds the largest subrange that is a max heap (C++11) (function template) http://cppreference.com 2024.06.10 std::ranges::is_heap_until(3)
NAME | Synopsis | Parameters | Return value | Complexity | Notes | Possible implementation | Example | Output: | See also
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