std::make_heap() algorithm
- since C++20
- until C++20
// (1)
template< class RandomIt >
constexpr void make_heap( RandomIt first, RandomIt last );
// (2)
template< class RandomIt, class Compare >
constexpr void make_heap( RandomIt first, RandomIt last, Compare comp );
// (1)
template< class RandomIt >
void make_heap( RandomIt first, RandomIt last );
// (2)
template< class RandomIt, class Compare >
void make_heap( RandomIt first, 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
.
-
(1) Elements are compared using
operator<
. -
(2) Elements are compared using the given binary comparison function
comp
.
Parameters
first last | The range of elements to make a heap from. |
policy | The execution policy to use. See execution policy for details. |
comp | Comparison function object (i.e. an object that satisfies the requirements of Compare). The signature of the comparison function should be equivalent to the following:
|
Type requirements
RandomIt | LegacyRandomAccessIterator |
The type defereferenced RandomIt | MoveAssignable MoveConstructible |
Return value
(none)
Complexity
Given N
as std::distance(first, last)
:
At most log(N) comparisons.
Exceptions
The overloads with a template parameter named ExecutionPolicy
report errors as follows:
- If execution of a function invoked as part of the algorithm throws an exception and
ExecutionPolicy
is one of the standard policies,std::terminate
is called. For any otherExecutionPolicy
, the behavior is implementation-defined. - If the algorithm fails to allocate memory,
std::bad_alloc
is thrown.
Notes
A max heap is a range of elements [f
; l
) that has the following properties:
- Given
N
asl - f
, for all0 < i < N
,f[(i - 1) / 2]
does not compare less thanf[i]
. - A new element can be added using
std::push_heap
, in O(log(N)) time. - The first element can be removed using
std::pop_heap
, in O(log(N)) time.
Examples
#include <algorithm>
#include <iostream>
#include <string_view>
#include <vector>
void println(std::string_view rem, std::vector<int> const& v)
{
std::cout << rem;
for (int e : v)
std::cout << e << ' ';
std::cout << '\n';
}
int main()
{
std::vector<int> v {3, 1, 4, 1, 5, 9};
std::make_heap(v.begin(), v.end());
println("after make_heap: ", v);
v.push_back(6);
println("after push_back: ", v);
std::push_heap(v.begin(), v.end());
println("after push_heap: ", v);
}
after make_heap: 9 5 4 1 1 3
after push_back: 9 5 4 1 1 3 6
after push_heap: 9 5 6 1 1 3 4
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