std::ranges::make_heap
Defined in header <algorithm> |
||
---|---|---|
Call signature | ||
template< std::random_access_iterator I, std::sentinel_for<I> S, class Comp = ranges::less, class Proj = std::identity > requires std::sortable<I, Comp, Proj> constexpr I make_heap( I first, S last, Comp comp = {}, Proj proj = {} ); |
(1) | (since C++20) |
template< ranges::random_access_range R, class Comp = ranges::less, class Proj = std::identity > requires std::sortable<ranges::iterator_t<R>, Comp, Proj> constexpr ranges::borrowed_iterator_t<R> make_heap( R&& r, Comp comp = {}, Proj proj = {} ); |
(2) | (since C++20) |
Constructs a max heap in the range [first, last)
.
1) Elements are compared using the given binary comparison function
comp
and projection object
proj
.
2) Same as
(1), but uses
r
as the range, as if using
ranges::begin(r)
as
first
and
ranges::end(r)
as
last
.
The function-like entities described on this page are niebloids, that is:
- Explicit template argument lists may not be specified when calling any of them.
- None of them is visible to argument-dependent lookup.
- When one of them is found by normal unqualified lookup for the name to the left of the function-call operator, it inhibits argument-dependent lookup.
In practice, they may be implemented as function objects, or with special compiler extensions.
Parameters
first, last | - | the range of elements to make the heap from |
r | - | the range of elements to make the heap from |
pred | - | predicate to apply to the projected elements |
proj | - | projection to apply to the elements |
Return value
An iterator equal to last
.
Complexity
Given N = ranges::distance(first, last)
, at most \(\scriptsize 3\cdot N\)3•N comparisons and \(\scriptsize 6\cdot N\)6•N projections.
Notes
A max heap is a range of elements [f, l)
, arranged with respect to comparator comp
and projection proj
, that has the following properties:
- With
N = l-f
,p = f[(i-1)/2]
, andq = f[i]
, for all0 < i < N
, the expressionstd::invoke(comp, std::invoke(proj, p), std::invoke(proj, q))
evaluates tofalse
. - A new element can be added using
ranges::push_heap
, in \(\scriptsize \mathcal{O}(\log N)\)𝓞(log N) time. - The first element can be removed using
ranges::pop_heap
, in \(\scriptsize \mathcal{O}(\log N)\)𝓞(log N) time.
Example
#include <algorithm> #include <vector> #include <cmath> #include <functional> #include <iostream> void draw_heap(auto const& v); void out(const auto& what, int n = 1) { while (n-- > 0) std::cout << what; } void print(auto rem, auto const& v) { out(rem); for (auto e : v) { out(e), out(' '); } out('\n'); } int main() { std::vector h {1, 6, 1, 8, 0, 3, 3, 9, 8, 8, 7, 4, 9, 8, 9}; print("source: ", h); std::ranges::make_heap(h); print("\n" "max-heap: ", h); draw_heap(h); std::ranges::make_heap(h, std::greater{}); print("\n" "min-heap: ", h); draw_heap(h); } void draw_heap(auto const& v) { auto bails = [](int n, int w) { auto b = [](int w) { out("┌"), out("─", w), out("┴"), out("─", w), out("┐"); }; if (!(n /= 2)) 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()); } }
Output:
source: 1 6 1 8 0 3 3 9 8 8 7 4 9 8 9 max-heap: 9 8 9 8 8 4 9 6 1 0 7 1 3 8 3 9 ┌───┴───┐ 8 9 ┌─┴─┐ ┌─┴─┐ 8 8 4 9 ┌┴┐ ┌┴┐ ┌┴┐ ┌┴┐ 6 1 0 7 1 3 8 3 min-heap: 0 1 1 8 6 3 3 9 8 8 7 4 9 8 9 0 ┌───┴───┐ 1 1 ┌─┴─┐ ┌─┴─┐ 8 6 3 3 ┌┴┐ ┌┴┐ ┌┴┐ ┌┴┐ 9 8 8 7 4 9 8 9
See also
(C++20)
|
checks if the given range is a max heap (niebloid) |
(C++20)
|
finds the largest subrange that is a max heap (niebloid) |
(C++20)
|
adds an element to a max heap (niebloid) |
(C++20)
|
removes the largest element from a max heap (niebloid) |
(C++20)
|
turns a max heap into a range of elements sorted in ascending order (niebloid) |
creates a max heap out of a range of elements (function template) |
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