std::pop_heap

 

C++

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Technical Specifications

 

Algorithm library

Functions
Non-modifying sequence operations
all_ofany_ofnone_of (C++11)(C++11)(C++11) for_each countcount_if mismatch equal	findfind_iffind_if_not (C++11) find_end find_first_of adjacent_find search search_n
Modifying sequence operations
copycopy_if (C++11) copy_n (C++11) copy_backward move (C++11) move_backward (C++11) fill fill_n transform generate generate_n removeremove_if remove_copyremove_copy_if	replacereplace_if replace_copyreplace_copy_if swap swap_ranges iter_swap reverse reverse_copy rotate rotate_copy random_shuffleshuffle (until C++17)(C++11) unique unique_copy
Partitioning operations
is_partitioned (C++11) partition partition_copy (C++11)	stable_partition partition_point (C++11)
Sorting operations (on sorted ranges)
is_sorted (C++11) is_sorted_until (C++11) sort	partial_sort partial_sort_copy stable_sort nth_element
Binary search operations (on sorted ranges)
lower_bound upper_bound	binary_search equal_range
Set operations (on sorted ranges)
merge inplace_merge includes	set_difference set_intersection set_symmetric_difference set_union
Heap operations
is_heap (C++11) is_heap_until (C++11) make_heap	push_heap pop_heap sort_heap
Minimum/maximum operations
max max_element min min_element minmax (C++11) minmax_element (C++11)	lexicographical_compare is_permutation (C++11) next_permutation prev_permutation
Numeric operations
iota (C++11) accumulate inner_product	adjacent_difference partial_sum
C library
qsort	bsearch

 

Defined in header <algorithm>
template< class RandomIt > void pop_heap( RandomIt first, RandomIt last );	(1)
template< class RandomIt, class Compare > void pop_heap( RandomIt first, RandomIt 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 max 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.

Parameters

first, last	-	the range of elements defining the valid nonempty heap to modify
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 ValueSwappable and RandomAccessIterator.
- The type of dereferenced RandomIt must meet the requirements of MoveAssignable and MoveConstructible.

Return value

(none)

Complexity

At most 2×log(N) comparisons where N=std::distance(first, 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

Run this code

#include <iostream>
#include <algorithm>
#include <vector>
 
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

See also

push_heap	adds an element to a max heap (function template)
make_heap	creates a max heap out of a range of elements (function template)