std::ranges::is_heap
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Constrained algorithms
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std::ranges
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Defined in header
<algorithm>
Call signature
template< std::random_access_iterator I, std::sentinel_for <I> S,
(1)
(since C++20)
class Proj = std::identity,
std::indirect_strict_weak_order
<std::projected <I, Proj>> Comp = ranges::less >
template< ranges::random_access_range R, class Proj = std::identity,
(2)
(since C++20)
std::indirect_strict_weak_order
<std::projected
<ranges::iterator_t <R>, Proj>> Comp = ranges::less >
Checks whether the specified range 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.
[edit] Parameters
first, last
-
the iterator-sentinel pair defining the range of elements to examine
r
-
the
range of elements to examine
comp
-
comparator to apply to the projected elements
proj
-
projection to apply to the elements
[edit] Return value
1) ranges::is_heap_until (first, last, comp, proj) == last
2) ranges::is_heap_until (r, comp, proj) == ranges::end (r)
[edit] Complexity
\(\scriptsize O(N) \)O(N) applications of comp and proj, where \(\scriptsize N \)N is:
1) ranges::distance (first, last)
2) ranges::distance (r)
[edit] 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::end (r), std::move(comp), std::move(proj)); } }; inline constexpr is_heap_fn is_heap{};
[edit] Example
Run this code
#include <algorithm> #include <bit> #include <cmath> #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); }; const int m{static_cast<int>(std::ceil (std::log2 (1 + v.size())))}; auto first{v.cbegin()}; for (int i{}; 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
[edit] See also
(C++20)
(algorithm function object)[edit]