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std::ranges::make_heap

From cppreference.com
< cpp‎ | algorithm‎ | ranges
 
 
Algorithm library
Constrained algorithms and algorithms on ranges (C++20)
Constrained algorithms, e.g. std::ranges::copy, std::ranges::sort, ...
Execution policies (C++17)
Non-modifying sequence operations
(C++11)(C++11)(C++11)
(C++17)
Modifying sequence operations
Partitioning operations
Sorting operations
(C++11)
Binary search operations
Set operations (on sorted ranges)
Heap operations
(C++11)
Minimum/maximum operations
(C++11)
(C++17)

Permutations
Numeric operations
Operations on uninitialized storage
(C++17)
(C++17)
(C++17)
C library
 
Constrained algorithms
Non-modifying sequence operations
Modifying sequence operations
Partitioning operations
Sorting operations
Binary search operations
Set operations (on sorted ranges)
Heap operations
ranges::make_heap
Minimum/maximum operations
Permutations
Operations on uninitialized storage
Return types
 
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:

In practice, they may be implemented as function objects, or with special compiler extensions.

Contents

[edit] 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

[edit] Return value

An iterator equal to last.

[edit] Complexity

Given N = ranges::distance(first, last), at most 3β€’N comparisons and 6β€’N projections.

[edit] Notes

The 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, for all 0 < i < N, p == f[(i - 1) / 2], and q == f[i], 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 π“ž(log N) time.
  • the first element can be removed using ranges::pop_heap(), in π“ž(log N) time.

[edit] 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("β”Œ"), out("─", w), out("β”΄"), 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
   β”Œβ”€β”€β”€β”΄β”€β”€β”€β”
   8       9
 β”Œβ”€β”΄β”€β”   β”Œβ”€β”΄β”€β”
 8   8   4   9
β”Œβ”΄β” β”Œβ”΄β” β”Œβ”΄β” β”Œβ”΄β”
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
   β”Œβ”€β”€β”€β”΄β”€β”€β”€β”
   1       1
 β”Œβ”€β”΄β”€β”   β”Œβ”€β”΄β”€β”
 8   6   3   3
β”Œβ”΄β” β”Œβ”΄β” β”Œβ”΄β” β”Œβ”΄β”
9 8 8 7 4 9 8 9

[edit] See also

checks if the given range is a max heap
(niebloid) [edit]
finds the largest subrange that is a max heap
(niebloid) [edit]
adds an element to a max heap
(niebloid) [edit]
removes the largest element from a max heap
(niebloid) [edit]
turns a max heap into a range of elements sorted in ascending order
(niebloid) [edit]
creates a max heap out of a range of elements
(function template) [edit]