std::is_heap(3)

NAME
std::is_heap - std::is_heap

Synopsis
   Defined in header <algorithm>
   template< class RandomIt > (1) (since C++11)
   bool is_heap( RandomIt first, RandomIt last ); (constexpr since C++20)
   template< class ExecutionPolicy, class RandomIt >
   bool is_heap( ExecutionPolicy&& policy, (2) (since C++17)
                 RandomIt first, RandomIt last );
   template< class RandomIt, class Compare > (since C++11)
   bool is_heap( RandomIt first, RandomIt last, Compare (3) (constexpr since C++20)
   comp );
   template< class ExecutionPolicy, class RandomIt, class
   Compare >
   bool is_heap( ExecutionPolicy&& policy, (4) (since C++17)
                 RandomIt first, RandomIt last, Compare
   comp );
   Checks whether [first, last) is a heap.
   1) The heap property to be checked is with respect to
   operator<
   (until C++20)
   std::less{}
   (since C++20).
   3) The heap property to be checked is with respect to comp.
   2,4) Same as (1,3), but executed according to policy.
   These overloads participate in overload resolution only if
   std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true. (until
                        C++20)
   std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>> is true. (since
                        C++20)

Parameters
   first, last - the range to be checked
   policy - the execution policy to use. See execution policy for details.
                  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.
   -
   Compare must meet the requirements of Compare.

Return value
   true if the range is a heap with respect to the corresponding comparator, false
   otherwise.

Complexity
   Given \(\scriptsize N\)N as std::distance(first, last):
   1,2) \(\scriptsize O(N)\)O(N) comparisons using
   operator<
   (until C++20)
   std::less{}
   (since C++20).
   3,4) \(\scriptsize O(N)\)O(N) applications of the comparison function comp.

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 other ExecutionPolicy, the behavior is implementation-defined.
     * If the algorithm fails to allocate memory, std::bad_alloc is thrown.

Example
// Run this code
 #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 (const 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}; const 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 |

See also
   is_heap_until finds the largest subrange that is a max heap
   (C++11) (function template)
   make_heap creates a max heap out of a range of elements
                   (function template)
   push_heap adds an element to a max heap
                   (function template)
   pop_heap removes the largest element from a max heap
                   (function template)
   sort_heap turns a max heap into a range of elements sorted in ascending order
                   (function template)
   ranges::is_heap checks if the given range is a max heap
   (C++20) (niebloid)