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 <std::projected<I, Proj>> Comp = ranges::less > constexpr bool is_heap( I first, S last, Comp comp = {}, Proj proj = {} ); |
(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>> Comp = ranges::less > constexpr bool is_heap( R&& r, Comp comp = {}, Proj proj = {} ); |
(2) | (since C++20) |
Checks whether the specified range represents a heap with respect to comp and proj.
1) The specified range is
[first, last).2) The specified range is
r.The function-like entities described on this page are algorithm function objects (informally known as 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.
Parameters
| first, last | - | the iterator-sentinel pair defining the range of elements to examine |
| r | - | the range of elements to examine
|
| comp | - | comparator to apply to the projected elements |
| proj | - | projection to apply to the elements |
Return value
1)
ranges::is_heap_until(first, last, comp, proj) == last2)
ranges::is_heap_until(r, comp, proj) == ranges::end(r)Complexity
O(N) applications of comp and proj, where N is:
1)
ranges::distance(first, last)2)
ranges::distance(r)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{};
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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(const auto& 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());
}
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);
}
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 1
See also
(C++20) |
finds the largest subrange that is a max heap (algorithm function object) |
(C++20) |
creates a max heap out of a range of elements (algorithm function object) |
(C++20) |
adds an element to a max heap (algorithm function object) |
(C++20) |
removes the largest element from a max heap (algorithm function object) |
(C++20) |
turns a max heap into a range of elements sorted in ascending order (algorithm function object) |
(C++11) |
checks if the given range is a max heap (function template) |