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
< std::projected<I, Proj>> Comp = ranges::less >
constexpr I is_heap_until( 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 ranges::borrowed_iterator_t<R>
is_heap_until( 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 >
I is_heap_until( 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 >
ranges::borrowed_iterator_t<R>
is_heap_until( 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) Examines the target range
[first, last) or r and finds the largest range which begins at first or ranges::begin(r) and represents a heap with respect to comp and proj.Within the specified range, finds the longest range which starting from the beginning of the specified range and 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
The past-the-end iterator of the largest range found.
Complexity
Given N as ranges::distance(first, last) or ranges::distance(r):
1-4) 𝓞(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).
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::next(ranges::begin(r), ranges::end(r)),
std::move(comp), std::move(proj));
}
};
inline constexpr is_heap_until_fn is_heap_until{};
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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
(C++11) |
finds the largest subrange that is a max heap (function template) |
(C++20) |
checks if the given range 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) |