std::is_heap
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 if the elements in range [first, last)
are a max heap.
operator<
.comp
.policy
. These overloads do not participate in overload resolution unless std::is_execution_policy_v<std::decay_t<ExecutionPolicy>>
is trueParameters
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. |
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 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:
- With
N = l - f
, for all0 < i < N
,f[floor(
does not compare less thani-1 2 f[i]
. - a new element can be added using
std::push_heap()
- the first element can be removed using
std::pop_heap()
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'; 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
(C++11) | finds the largest subrange that is a max heap (function template) |
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