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 = {} );
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(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 = {} );
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(2) | (since C++20) |
template< /*execution-policy*/ Ep,
std::random_access_iterator I, std::sized_sentinel_for<I> S,
class Proj = std::identity,
std::indirect_strict_weak_order
<std::projected<I, Proj>> Comp = ranges::less >
bool is_heap( Ep&& policy, I first, S last, Comp comp = {}, Proj proj = {} );
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(3) | (since C++26) |
template< /*execution-policy*/ Ep, /*sized-random-access-range*/ R,
class Proj = std::identity,
std::indirect_strict_weak_order
<std::projected<ranges::iterator_t<R>,
Proj>> Comp = ranges::less >
bool ranges::is_heap( Ep&& policy, R&& r, Comp comp = {}, Proj proj = {} );
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(4) | (since C++26) |
For the definition of /*execution-policy*/, see this page; for the definition of /*sized-random-access-range*/, see this page.
1,2) Checks whether the target range
[first, last) or r represents a heap with respect to comp and proj.3,4) Same as (1,2), but executed according to
policy.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 target range |
| r | - | the target range |
| comp | - | the comparator to be applied to the (projected) elements |
| proj | - | the projection to be applied to the elements |
| policy | - | the execution policy to use |
Return value
true if the target range represents a heap with respect to comp and proj, false otherwise.
Complexity
Given \(\scriptsize N\)N as ranges::distance(first, last) or ranges::distance(r):
1-4) \(\scriptsize \mathcal{O}(N)\)(N) applications of
comp, and twice as many applications of proj.Exceptions
3,4) During the execution process:
- If the temporary memory resources required for parallelization are not available, std::bad_alloc is thrown.
- If an uncaught exception is thrown while accessing objects via an algorithm argument, the behavior is determined by the execution policy (for standard policies, std::terminate is invoked).
Notes
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_parallel_algorithm |
202506L |
(C++26) | Parallel range algorithms, overloads (3,4) |
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::next(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 <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);
};
auto first{v.cbegin()};
for (int i{}, m{std::bit_width(v.size())}; 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++11) |
checks if the given range is a max heap (function template) |
(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 sorted range of elements (algorithm function object) |