std::ranges::is_heap
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) |
Checks if the elements in range [first, last) are 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
true if the range is max heap, false otherwise.
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_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 bool operator()(I first, S last, Comp comp = {}, Proj proj = {}) const { return (last == ranges::is_heap_until(first, last, std::move(comp), std::move(proj))); } 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 bool 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_fn is_heap {}; |
Example
Run this code
#include <algorithm> #include <bit> #include <cmath> #include <iostream> #include <vector> void out(const auto& what, int n = 1) { while (n-- > 0) std::cout << what; } void draw_heap(auto const& v); int main() { std::vector<int> v {3, 1, 4, 1, 5, 9, 2, 6, 5, 3, 5, 8, 9, 7, 9, 3, 2, 3, 8}; out("initially, v:\n"); for (auto i : v) std::cout << i << ' '; out('\n'); if (!std::ranges::is_heap(v)) { out("making heap...\n"); std::ranges::make_heap(v); } out("after make_heap, v:\n"); for (auto t {1U}; auto i : v) std::cout << i << (std::has_single_bit(++t) ? " │ " : " "); out("\n" "corresponding binary tree is:\n"); draw_heap(v); } void draw_heap(auto const& v) { 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 int m {static_cast<int>(std::ceil(std::log2(1 + v.size())))}; auto first {v.cbegin()}; for (int i {}; i != m; ++i) tier(i, m, first, v.cend()); }
Output:
initially, v:
3 1 4 1 5 9 2 6 5 3 5 8 9 7 9 3 2 3 8
making heap...
after make_heap, v:
9 │ 8 9 │ 6 5 8 9 │ 3 5 3 5 3 4 7 2 │ 1 2 3 1
corresponding binary tree is:
9
┌───────┴───────┐
8 9
┌───┴───┐ ┌───┴───┐
6 5 8 9
┌─┴─┐ ┌─┴─┐ ┌─┴─┐ ┌─┴─┐
3 5 3 5 3 4 7 2
┌┴┐ ┌┴┐ ┌┴┐ ┌┴┐ ┌┴┐ ┌┴┐ ┌┴┐ ┌┴┐
1 2 3 1See also
| (C++20) |
finds the largest subrange that 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) |
checks if the given range is a max heap (function template) |