std::is_heap

 

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

Checks if the elements in range [first, last) are a 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); 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

Return value

true if the range is heap, false otherwise.

Complexity

Linear in the distance between first and last

Notes

A heap with respect to comp (max heap) is a random access range [first, last) that has the following properties:

• Given \(\scriptsize N\)N as last - first, for all integer i where \(\scriptsize 0 < i < N\)0 < i < N, bool(comp(first[(i - 1) / 2], first[i])) is false.
• A new element can be added using std::push_heap, in \(\scriptsize \mathcal{O}(\log N)\)𝓞(log N) time.
• *first can be removed using std::pop_heap, in \(\scriptsize \mathcal{O}(\log N)\)𝓞(log N) time.

Example

Run this code

#include <iostream>
#include <algorithm>
 
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

Template:cpp/algorithm/dcl list is heap until