std::ranges::push_heap
From cppreference.com
| 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 > |
(1) | (since C++20) |
| template< ranges::random_access_range R, class Comp = ranges::less, class Proj = std::identity > |
(2) | (since C++20) |
Inserts the element at the position last - 1 into the max heap defined by the range [first, last - 1).
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 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.
In practice, they may be implemented as function objects, or with special compiler extensions.
Parameters
| first, last | - | the range of elements defining the heap to modify |
| r | - | the range of elements defining the heap to modify |
| 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 log(N) comparisons and 2log(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 expression std::invoke(comp, std::invoke(proj, p), std::invoke(proj, q)) evaluates to false. - A new element can be added using ranges::push_heap, in 𝓞(log N) time.
- The first element can be removed using ranges::pop_heap, in 𝓞(log N) time.
- With
Possible implementation
struct push_heap_fn { 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 operator()(I first, S last, Comp comp = {}, Proj proj = {}) const { const auto n {ranges::distance(first, last)}; const auto length {n}; if (n > 1) { I last {first + n}; n = (n - 2) / 2; I i {first + n}; if (std::invoke(comp, std::invoke(proj, *i), std::invoke(proj, *--last))) { std::iter_value_t<I> v {ranges::iter_move(last)}; do { *last = ranges::iter_move(i); last = i; if (n == 0) break; n = (n - 1) / 2; i = first + n; } while (std::invoke(comp, std::invoke(proj, *i), std::invoke(proj, v))); *last = std::move(v); } } return first + length; } 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> operator()(R&& r, Comp comp = {}, Proj proj = {}) const { return (*this)(ranges::begin(r), ranges::end(r), std::move(comp), std::move(proj)); } }; inline constexpr push_heap_fn push_heap {}; |
Example
Run this code
#include <algorithm> #include <cmath> #include <iostream> #include <vector> 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'); } void draw_heap(auto const& v); int main() { std::vector<int> v {1, 6, 1, 8, 0, 3,}; print("source vector v: ", v); std::ranges::make_heap(v); print("after make_heap: ", v); draw_heap(v); v.push_back(9); print("before push_heap: ", v); draw_heap(v); std::ranges::push_heap(v); print("after push_heap: ", v); draw_heap(v); } 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 vector v: 1 6 1 8 0 3 after make_heap: 8 6 3 1 0 1 8 ┌─┴─┐ 6 3 ┌┴┐ ┌┴┐ 1 0 1 before push_heap: 8 6 3 1 0 1 9 8 ┌─┴─┐ 6 3 ┌┴┐ ┌┴┐ 1 0 1 9 after push_heap: 9 6 8 1 0 1 3 9 ┌─┴─┐ 6 8 ┌┴┐ ┌┴┐ 1 0 1 3
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) |
creates a max heap out of a range of elements (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) |
| adds an element to a max heap (function template) |