std::is_heap

Defined in header `<algorithm>`
template< class RandomIt > bool is_heap( RandomIt first, RandomIt last );	(1)	(since C++11)
template< class RandomIt, class Compare > bool is_heap( RandomIt first, RandomIt last, Compare comp );	(2)	(since C++11)

Checks if the elements in range [first, last) are a max heap.

The first version of is_heap uses operator< to compare elements, whereas the second uses the given comparison function comp.

Parameters

first, last	-	the range of elements to examine
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.

Notes

A max heap is a range of elements [f,l) that has the following properties:

*f is the largest element in the range
a new element can be added using std::push_heap()
the first element can be removed using std::pop_heap()

The actual arrangement of the elements is implementation defined.

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

is_heap_until (C++11)	finds the largest subrange that is a max heap (function template)
std::experimental::parallel::is_heap (parallelism TS)	parallelized version of `std::is_heap` (function template)