Defined in header <algorithm>  

(1)  
template< class RandomIt > bool is_heap( RandomIt first, RandomIt last );  (since C++11) (until C++20)  
template< class RandomIt > constexpr bool is_heap( RandomIt first, RandomIt last );  (since C++20)  
template< class ExecutionPolicy, class RandomIt > bool is_heap( ExecutionPolicy&& policy, RandomIt first, RandomIt last );  (2)  (since C++17) 
(3)  
template< class RandomIt, class Compare > bool is_heap( RandomIt first, RandomIt last, Compare comp );  (since C++11) (until C++20)  
template< class RandomIt, class Compare > constexpr bool is_heap( RandomIt first, RandomIt last, Compare comp );  (since C++20)  
template< class ExecutionPolicy, class RandomIt, class Compare > bool is_heap( ExecutionPolicy&& policy, RandomIt first, RandomIt last, Compare comp );  (4)  (since C++17) 
Checks whether the elements in range [
first
,
last
)
are a max heap.
operator<
.comp
.policy
. These overloads do not participate in overload resolution unless
 (until C++20) 
 (since C++20) 
first, last    the range of elements to examine 
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) which returns true if the first argument is less than the second. The signature of the comparison function should be equivalent to the following:
While the signature does not need to have 
Type requirements  
RandomIt must meet the requirements of LegacyRandomAccessIterator. 
true
if the range is max heap, false
otherwise.
Linear in the distance between first
and last
.
The overloads with a template parameter named ExecutionPolicy
report errors as follows:
ExecutionPolicy
is one of the standard policies, std::terminate
is called. For any other ExecutionPolicy
, the behavior is implementationdefined. std::bad_alloc
is thrown. A max heap is a range of elements [
f
,
l
)
that has the following properties:
N = l  f
, for all 0 < i < N
, f[(i  1) / 2]
does not compare less than f[i]
. std::push_heap
, in \(\scriptsize \mathcal{O}(\log N)\)𝓞(log N) time. std::pop_heap
, in \(\scriptsize \mathcal{O}(\log N)\)𝓞(log N) time. #include <algorithm> #include <bit> #include <iostream> #include <vector> int main() { std::vector<int> v {3, 1, 4, 1, 5, 9, 2, 6, 5, 3, 5, 8, 9, 7, 9}; std::cout << "initially, v:\n"; for (auto i : v) std::cout << i << ' '; std::cout << '\n'; if (!std::is_heap(v.begin(), v.end())) { std::cout << "making heap...\n"; std::make_heap(v.begin(), v.end()); } std::cout << "after make_heap, v:\n"; for (auto t{1U}; auto i : v) std::cout << i << (std::has_single_bit(++t) ? "  " : " "); std::cout << '\n'; }
Output:
initially, v: 3 1 4 1 5 9 2 6 5 3 5 8 9 7 9 making heap... after make_heap, v: 9  6 9  5 5 9 7  1 1 3 5 8 3 4 2 
(C++11)  finds the largest subrange that is a max heap (function template) 
creates a max heap out of a range of elements (function template) 

adds an element to a max heap (function template) 

removes the largest element from a max heap (function template) 

turns a max heap into a range of elements sorted in ascending order (function template) 

(C++20)  checks if the given range is a max heap (niebloid) 
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