std::make_heap (3) - Linux Manuals

std::make_heap: std::make_heap

NAME

std::make_heap - std::make_heap

Synopsis

Defined in header <algorithm>
template< class RandomIt > (until C++20)
void make_heap( RandomIt first, RandomIt last );
template< class RandomIt > (since C++20)
constexpr void make_heap( RandomIt first, RandomIt last );
template< class RandomIt, class Compare > (1)
void make_heap( RandomIt first, RandomIt last, (until C++20)
Compare comp ); (2)
template< class RandomIt, class Compare >
constexpr void make_heap( RandomIt first, RandomIt last, (since C++20)
Compare comp );

Constructs a max heap in 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 to make the heap from
              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);
comp - 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

-
RandomIt must meet the requirements of LegacyRandomAccessIterator.
-
The type of dereferenced RandomIt must meet the requirements of MoveAssignable and MoveConstructible.

Return value

(none)

Complexity

At most 3*std::distance(first, last) comparisons.

Notes

A max heap is a range of elements [f,l) that has the following properties:

Example

// Run this code

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

  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';

      std::make_heap(v.begin(), v.end());

      std::cout << "after make_heap, v: ";
      for (auto i : v) std::cout << i << ' ';
      std::cout << '\n';

      std::pop_heap(v.begin(), v.end());
      auto largest = v.back();
      v.pop_back();
      std::cout << "largest element: " << largest << '\n';

      std::cout << "after removing the largest element, v: ";
      for (auto i : v) std::cout << i << ' ';
      std::cout << '\n';
  }

Output:

  initially, v: 3 1 4 1 5 9
  after make_heap, v: 9 5 4 1 1 3
  largest element: 9
  after removing the largest element, v: 5 3 4 1 1