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std::pop_heap

From cppreference.com
 
 
 
Defined in header <algorithm>
template< class RandomAccessIterator >
void pop_heap( RandomAccessIterator first, RandomAccessIterator last );
(1)
template< class RandomAccessIterator, class Compare >

void pop_heap( RandomAccessIterator first, RandomAccessIterator last,

               Compare comp );
(2)

Swaps the value in the position first and the value in the position last-1 and makes the subrange [first, last-1) into a heap. This has the effect of removing the first (largest) element from the heap defined by the range [first, last).

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 defining the valid nonempty heap to modify
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

(none)

[edit] Complexity

At most 2×log(N) comparisons where N=std::distance(first, 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());
 
    std::cout << "v: ";
    for (auto i : v) std::cout << i << ' ';
    std::cout << '\n';
 
    std::pop_heap(v.begin(), v.end()); // moves the largest to the end
 
    std::cout << "after pop_heap: ";
    for (auto i : v) std::cout << i << ' ';
    std::cout << '\n';
 
    int largest = v.back();
    v.pop_back();  // actually removes the largest element
    std::cout << "largest element: " << largest << '\n';
 
    std::cout << "heap without largest: ";
    for (auto i : v) std::cout << i << ' ';
    std::cout << '\n';
}

Output:

v: 9 5 4 1 1 3 
after pop_heap: 5 3 4 1 1 9 
largest element: 9
heap without largest: 5 3 4 1 1

[edit] See also

adds an element to a heap
(function template) [edit]