View source for cpp/algorithm/ranges/is heap until

You do not have permission to edit this page, for the following reason:

Due to recent vandalism, editing of this page is temporarily disabled for new users.If you want to suggest a change, please leave a message on the suggestions page for new users instead (don't be surprised if that page appears vandalized!).

You can view and copy the source of this page:

{{cpp/ranges/title|is_heap_until}}
{{cpp/algorithm/ranges/navbar}}
{{dcl begin}}
{{dcl header|algorithm}}
{{dcl h|Call signature}}
{{dcl|num=1|since=c++20|1=
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 = {} );
}}
{{dcl|num=2|since=c++20|1=
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 = {} );
}}
{{dcl end}}

Within the specified range, finds the longest range which starting from the beginning of the specified range and represents a [[cpp/algorithm#Heap operations|heap]] with respect to {{c|comp}} and {{c|proj}}.

@1@ The specified range is {{range|first|last}}.

@2@ The specified range is {{c|r}}.

{{cpp/ranges/niebloid}}

===Parameters===
{{par begin}}
{{par|first, last|the range of elements to examine}}
{{par|r|the range of elements to examine}}
{{par|pred|predicate to apply to the projected elements}}
{{par|proj|projection to apply to the elements}}
{{par end}}

===Return value===
The last iterator {{c|iter}} in the specified range for which:
@1@ The range {{range|first|iter}} is a heap with respect to {{c|comp}} and {{c|proj}}.
@2@ The range {{range|ranges::begin(r)|iter}} is a heap with respect to {{c|comp}} and {{c|proj}}.

===Complexity===
{{mathjax-or|\(\scriptsize O(N) \)|O(N)}} applications of {{c|comp}} and {{c|proj}}, where {{mathjax-or|\(\scriptsize N \)|N}} is:
@1@ {{c|ranges::distance(first, last)}}
@2@ {{c|ranges::distance(r)}}

===Possible implementation===
{{eq fun|1=
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===
{{example
|The example renders a given vector as a (balanced) {{enwiki|Binary tree}}.
|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=<nowiki/>
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===
{{dsc begin}}
{{dsc inc|cpp/algorithm/ranges/dsc is_heap}}
{{dsc inc|cpp/algorithm/ranges/dsc make_heap}}
{{dsc inc|cpp/algorithm/ranges/dsc push_heap}}
{{dsc inc|cpp/algorithm/ranges/dsc pop_heap}}
{{dsc inc|cpp/algorithm/ranges/dsc sort_heap}}
{{dsc inc|cpp/algorithm/dsc is_heap_until}}
{{dsc end}}

{{langlinks|de|es|fr|it|ja|pt|ru|zh}}

Templates used on this page:

Template:! (view source) (protected)
Template:!- (edit)
Template:= (edit)
Template:box/core (edit)
Template:c (view source) (protected)
Template:c/core (view source) (protected)
Template:cpp/algorithm/dsc is heap until (edit)
Template:cpp/algorithm/navbar content (edit)
Template:cpp/algorithm/navbar heading (edit)
Template:cpp/algorithm/ranges/dsc is heap (edit)
Template:cpp/algorithm/ranges/dsc make heap (edit)
Template:cpp/algorithm/ranges/dsc pop heap (edit)
Template:cpp/algorithm/ranges/dsc push heap (edit)
Template:cpp/algorithm/ranges/dsc sort heap (edit)
Template:cpp/algorithm/ranges/navbar (edit)
Template:cpp/algorithm/ranges/navbar content (edit)
Template:cpp/algorithm/ranges/navbar heading (edit)
Template:cpp/navbar content (edit)
Template:cpp/navbar heading (edit)
Template:cpp/ranges/niebloid (edit)
Template:cpp/ranges/title (edit)
Template:cpp/title (view source) (protected)

cppreference.com

Namespaces

Variants

Views

Actions

View source for cpp/algorithm/ranges/is heap until