make_heap


Category: algorithms	Component type: function

Prototype

Make_heap is an overloaded name; there are actually two make_heap functions.

template <class RandomAccessIterator>
void make_heap(RandomAccessIterator first
RandomAccessIterator last);

template <class RandomAccessIterator
class StrictWeakOrdering>
void make_heap(RandomAccessIterator first
RandomAccessIterator last

               StrictWeakOrdering comp);

Description

Make_heap turns the range [first last) into a heap [1].

The two versions of make_heap differ in how they define whether one element is less than another. The first version compares objects using operator< and the second compares objects using a function object comp. In the first version the postcondition is that is_heap(first last) is true and in the second version the postcondition is that is_heap(first last comp) is true.

Definition

Defined in the standard header algorithm and in the nonstandard backward-compatibility header algo.h.

Requirements on types

For the first version:

RandomAccessIterator is a model of Random Access Iterator.
RandomAccessIterator is mutable.
RandomAccessIterator's value type is a model of LessThan Comparable.
The ordering on objects of RandomAccessIterator's value type is a strict weak ordering as defined in the LessThan Comparable requirements.

For the second version:

RandomAccessIterator is a model of Random Access Iterator.
RandomAccessIterator is mutable.
StrictWeakOrdering is a model of Strict Weak Ordering.
RandomAccessIterator's value type is convertible to StrictWeakOrdering's argument type.

Preconditions

[first last) is a valid range.

Complexity

Linear. At most 3*(last - first) comparisons.

Example

int main()
{
  int A[] = {1
4
2
8
5
7};
  const int N = sizeof(A) / sizeof(int);

  make_heap(A
A+N);
  copy(A
A+N
ostream_iterator<int>(cout
" "));
  cout << endl;

  sort_heap(A
A+N);
  copy(A
A+N
ostream_iterator<int>(cout
" "));
  cout << endl;
}

Notes

[1] A heap is a particular way of ordering the elements in a range of Random Access Iterators [f l). The reason heaps are useful (especially for sorting or as priority queues) is that they satisfy two important properties. First *f is the largest element in the heap. Second it is possible to add an element to a heap (using push_heap) or to remove *f in logarithmic time. Internally a heap is simply a tree represented as a sequential range. The tree is constructed so that that each node is less than or equal to its parent node.