NAME

std::push_heap - std::push_heap

Synopsis

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

void push_heap( RandomIt first, RandomIt last, (1) (until C++20)

Compare comp );
template< class RandomIt, class Compare > (2)

constexpr void push_heap( RandomIt first, (since C++20)
RandomIt last,

Compare comp );

Inserts the element at the position last-1 into the max heap defined by the range
[first, last-1). 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 defining the heap to modify
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);
comp -
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 log(N) comparisons where N=std::distance(first, last).

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[(i-1)/2] does not compare less than
f[i].
* A new element can be added using std::push_heap, in \(\scriptsize
\mathcal{O}(\log N)\)𝓞(log N) time.
* The first element can be removed using std::pop_heap, in \(\scriptsize
\mathcal{O}(\log N)\)𝓞(log N) time.

Example

// Run this code

#include <iostream>
#include <algorithm>
#include <vector>

int main()
{
std::vector<int> v { 3, 1, 4, 1, 5, 9 };

std::make_heap(v.begin(), v.end());

std::cout << "v: ";
for (auto i : v) std::cout << i << ' ';
std::cout << '\n';

v.push_back(6);

std::cout << "before push_heap: ";
for (auto i : v) std::cout << i << ' ';
std::cout << '\n';

std::push_heap(v.begin(), v.end());

std::cout << "after push_heap: ";
for (auto i : v) std::cout << i << ' ';
std::cout << '\n';
}

Output:

v: 9 5 4 1 1 3
before push_heap: 9 5 4 1 1 3 6
after push_heap: 9 5 6 1 1 3 4