std::make_heap
Defined in header <algorithm>
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(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, |
(until C++20) | |
template< class RandomIt, class Compare > constexpr void make_heap( RandomIt first, RandomIt last, |
(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) |
Type requirements | ||
-RandomIt must meet the requirements of LegacyRandomAccessIterator.
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-The type of dereferenced RandomIt must meet the requirements of MoveAssignable and MoveConstructible.
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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 all0 < i < N
,f[floor(
does not compare less than
)]i-1 2 f[i]
. - a new element can be added using std::push_heap()
- the first element can be removed using std::pop_heap()
- With
Example
#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
turns a max heap into a range of elements sorted in ascending order (function template) | |
adapts a container to provide priority queue (class template) | |
function object implementing x > y (class template) |