std::is_heap_until

 

C++

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uninitialized_copy uninitialized_move (C++17)    uninitialized_fill uninitialized_copy_n (C++11) uninitialized_move_n (C++17) uninitialized_fill_n	destroy (C++17) destroy_n (C++17) destroy_at (C++17) construct_at (C++20)       uninitialized_default_construct (C++17) uninitialized_value_construct (C++17) uninitialized_default_construct_n (C++17) uninitialized_value_construct_n (C++17)

 

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

Examines the range [first, last) and finds the largest range beginning at first which is heap. The first version of the function uses operator< to compare the elements, 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

The upper bound of the largest range beginning at first which is heap. That is, the last iterator it for which range [first, it) is heap.

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::make_heap(v.begin(), v.end());
 
    // probably mess up the heap
    v.push_back(2);
    v.push_back(6);
 
    auto heap_end = std::is_heap_until(v.begin(), v.end());
 
    std::cout << "all of v: ";
    for (auto i : v) std::cout << i << ' ';
    std::cout << '\n';
 
    std::cout << "only heap: ";
    for (auto i = v.begin(); i != heap_end; ++i) std::cout << *i << ' ';
    std::cout << '\n';
}

Output:

all of v:  9 5 4 1 1 3 2 6 
only heap: 9 5 4 1 1 3 2

See also

is_heap (C++11)

checks if the given range is a max heap (function template)