std::make_heap

 

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Technical Specifications

 

Algorithm library

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is_execution_policy	execution::seqexecution::parexecution::par_unseq	execution::sequenced_policyexecution::parallel_policyexecution::parallel_unsequenced_policy
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all_ofany_ofnone_of (C++11)(C++11)(C++11) for_each for_each_n (C++17)	countcount_if mismatch equal adjacent_find	findfind_iffind_if_not (C++11) find_end find_first_of	search search_n lexicographical_compare lexicographical_compare_3way (C++20)
Modifying sequence operations
copycopy_if (C++11) copy_n (C++11) copy_backward move (C++11) move_backward (C++11) shift_leftshift_right (C++20)(C++20) transform	fill fill_n generate generate_n swap iter_swap swap_ranges sample (C++17)	removeremove_if replacereplace_if reverse rotate unique random_shuffle (until C++17)	remove_copyremove_copy_if replace_copyreplace_copy_if reverse_copy rotate_copy unique_copy shuffle (C++11)
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is_heap (C++11) is_heap_until (C++11)	make_heap sort_heap	push_heap pop_heap
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max max_element	min min_element	minmax (C++11) minmax_element (C++11)	clamp (C++17) compare_3way (C++20)
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C library
qsort	bsearch

 

Defined in header <algorithm>
	(1)
template< class RandomIt > void make_heap( RandomIt first, RandomIt last );			(until C++20)
template< class RandomIt > constexpr void make_heap( RandomIt first, RandomIt last );			(since C++20)
		(2)
template< class RandomIt, class Compare > void make_heap( RandomIt first, RandomIt last,                 Compare comp );				(until C++20)
template< class RandomIt, class Compare > constexpr void make_heap( RandomIt first, RandomIt last,                           Compare comp );				(since C++20)

Constructs a max heap in the range [first, last). The first version of the function uses operator< to compare the elements, the second uses the given comparison function comp.

Parameters

first, last	-	the range of elements to make the heap from
comp	-	comparison function object (i.e. an object that satisfies the requirements of Compare) which returns ​true if the first argument is less than the second. The signature of the comparison function should be equivalent to the following:  bool cmp(const Type1 &a, const Type2 &b); While the signature does not need to have const &, the function must not modify the objects passed to it and must be able to accept all values of type (possibly const) Type1 and Type2 regardless of value category (thus, Type1 & is not allowed, nor is Type1 unless for Type1 a move is equivalent to a copy (since C++11)). The types Type1 and Type2 must be such that an object of type RandomIt can be dereferenced and then implicitly converted to both of them. ​
Type requirements
- RandomIt must meet the requirements of LegacyRandomAccessIterator.
- The type of dereferenced RandomIt must meet the requirements of MoveAssignable and MoveConstructible.

Return value

(none)

Complexity

At most 3*std::distance(first, last) comparisons.

Notes

A max heap is a range of elements [f,l) that has the following properties:

• With N = l - f, for all 0 < i < N, f[floor(

  i-1

  2

  )] does not compare less than f[i].
• a new element can be added using std::push_heap()
• the first element can be removed using std::pop_heap()

Example

Run this code

#include <iostream>
#include <algorithm>
#include <vector>
 
int main()
{
    std::vector<int> v { 3, 1, 4, 1, 5, 9 };
 
    std::cout << "initially, v: ";
    for (auto i : v) std::cout << i << ' ';
    std::cout << '\n';
 
    std::make_heap(v.begin(), v.end());
 
    std::cout << "after make_heap, v: ";
    for (auto i : v) std::cout << i << ' ';
    std::cout << '\n';
 
    std::pop_heap(v.begin(), v.end());
    auto largest = v.back();
    v.pop_back();
    std::cout << "largest element: " << largest << '\n';
 
    std::cout << "after removing the largest element, v: ";
    for (auto i : v) std::cout << i << ' ';
    std::cout << '\n';
}

Output:

initially, v: 3 1 4 1 5 9 
after make_heap, v: 9 5 4 1 1 3 
largest element: 9
after removing the largest element, v: 5 3 4 1 1

See also

sort_heap	turns a max heap into a range of elements sorted in ascending order (function template)
priority_queue	adapts a container to provide priority queue (class template)
greater	function object implementing x > y (class template)