std::ranges::is_heap_until - cppreference.com (original) (raw)

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.

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.

Contents

• 1 Parameters
• 2 Return value
• 3 Complexity
• 4 Possible implementation
• 5 Example
• 6 See also

[edit] Parameters

[edit] Return value

The last iterator iter in the specified range for which:

1. The range [first, iter) is a heap with respect to comp and proj.

2. The range [ranges::begin(r), iter) is a heap with respect to comp and proj.

[edit] Complexity

\(\scriptsize O(N) \)O(N) applications of comp and proj, where \(\scriptsize N \)N is:

[edit] Possible implementation

struct is_heap_until_fn { template<std::random_access_iterator I, std::sentinel_for 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 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, Proj>> Comp = ranges::less> constexpr ranges::borrowed_iterator_t 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{};

[edit] Example

The example renders a given vector as a (balanced) Binary tree.

#include #include #include #include #include   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(std::ceil(std::log2(1 + size)))}; for (int i{}; i != m; ++i) tier(i, m, first, last); }   int main() { std::vector 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

[edit] See also