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std::is_heap_until

From cppreference.com
 
 
 
Defined in header <algorithm>
template< class RandomAccessIterator >

RandomAccessIterator is_heap_until( RandomAccessIterator first,

                                    RandomAccessIterator last );
(1) (since C++11)
template< class RandomAccessIterator, class Compare >

RandomAccessIterator is_heap_until( RandomAccessIterator first,
                                    RandomAccessIterator 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.

Contents

[edit] Parameters

first, last - the range of elements to examine
comp - comparison function 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 must not modify the objects passed to it.
The types  Type1 and  Type2 must be such that an object of type RandomAccessIterator can be dereferenced and then implicitly converted to both of them. ​

[edit] 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.

[edit] Complexity

linear in the distance between first and last

[edit] Notes

A 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.

[edit] Example

#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

[edit] See also

checks if the given range is a heap
(function template) [edit]