std::ranges::is_heap_until
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 Proj = std::identity, std::indirect_strict_weak_order< |
(1) | (since C++20) |
| template< ranges::random_access_range R, class Proj = std::identity, std::indirect_strict_weak_order<std::projected<ranges::iterator_t<R>, Proj>> |
(2) | (since C++20) |
Examines the range [first, last) and finds the largest range beginning 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::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.
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], andq = f[i], for all0 < i < N, the expression std::invoke(comp, std::invoke(proj, p), std::invoke(proj, q)) evaluates to false. - A new element can be added using ranges::push_heap, in 𝓞(log N) time.
- The first element can be removed using ranges::pop_heap, in 𝓞(log N) time.
- With
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_order< 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::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::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); 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); } 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); }
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 2See also
| (C++20) |
checks if the given range is a max heap (niebloid) |
| (C++20) |
creates a max heap out of a range of elements (niebloid) |
| (C++20) |
adds an element to a max heap (niebloid) |
| (C++20) |
removes the largest element from a max heap (niebloid) |
| (C++20) |
turns a max heap into a range of elements sorted in ascending order (niebloid) |
| (C++11) |
finds the largest subrange that is a max heap (function template) |