std::is_heap

 

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Technical Specifications

 

Algorithm library

Execution policies (C++17)
is_execution_policy	execution::seqexecution::parexecution::par_unseq	execution::sequenced_policyexecution::parallel_policyexecution::parallel_unsequenced_policy
Non-modifying sequence operations
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) 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)
Operations on uninitialized storage
uninitialized_copy uninitialized_move (C++17)	uninitialized_copy_n (C++11) uninitialized_move_n (C++17)	uninitialized_fill	uninitialized_fill_n
Partitioning operations
is_partitioned (C++11) partition_point (C++11)	partition partition_copy (C++11)	stable_partition
Sorting operations
is_sorted (C++11) is_sorted_until (C++11)	sort stable_sort	partial_sort partial_sort_copy	nth_element
Binary search operations
lower_bound	upper_bound	binary_search	equal_range
Set operations (on sorted ranges)
merge inplace_merge	set_difference set_intersection	set_symmetric_difference set_union	includes
Heap operations
is_heap (C++11) is_heap_until (C++11)	make_heap sort_heap	push_heap pop_heap
Minimum/maximum operations
max max_element	min min_element	minmax (C++11) minmax_element (C++11)	clamp (C++17) compare_3way (C++20)
Permutations
is_permutation (C++11)	next_permutation	prev_permutation
Numeric operations
iota (C++11) inner_product adjacent_difference	accumulate reduce (C++17) transform_reduce (C++17)	partial_sum inclusive_scan (C++17) exclusive_scan (C++17)	transform_inclusive_scan (C++17) transform_exclusive_scan (C++17)
C library
qsort	bsearch

 

Defined in header <algorithm>
	(1)
template<class RandomIt > bool is_heap( RandomIt first, RandomIt last );			(since C++11) (until C++20)
template<class RandomIt > constexprbool 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 > constexprbool 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 if the elements in range [first, last) are a max heap.

1) Elements are compared using operator<.

3) Elements are compared using the given binary comparison function comp.

2,4) Same as (1,3), but executed according to policy. These overloads do not participate in overload resolution unless std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true

Parameters

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:  bool cmp(const Type1 &a, const Type2 &b); The signature does not need to have const&, but the function object must not modify the objects passed to it. 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 RandomAccessIterator.

Return value

true if the range is max heap, false otherwise.

Complexity

Linear in the distance between first and last

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 three standard policies, std::terminate is called. For any other ExecutionPolicy, 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:

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

Output:

initially, v: 3 1 4 1 5 9 making heap... after make_heap, v: 9 5 4 1 1 3

See also

is_heap_until (C++11)

finds the largest subrange that is a max heap (function template)