std::ranges::is_heap_until
std::ranges
<algorithm>
class Proj = std::identity,
std::indirect_strict_weak_order
< std::projected <I, Proj>> Comp = ranges::less >
std::indirect_strict_weak_order
<std::projected
<ranges::iterator_t <R>, Proj>> Comp = ranges::less >
constexpr ranges::borrowed_iterator_t <R>
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.
[
first,
last)
.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.
[edit] Parameters
[edit] Return value
The last iterator iter in the specified range for which:
[
first,
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 <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{};
[edit] Example
The example renders a given vector as a (balanced) Binary tree.
#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
[edit] See also
(algorithm function object)[edit]