sort_heap


Category: algorithms	Component type: function

Prototype

Sort_heap is an overloaded name; there are actually two sort_heap functions.

template <class RandomAccessIterator>
void sort_heap(RandomAccessIterator first, RandomAccessIterator last);

template <class RandomAccessIterator, class StrictWeakOrdering>
void sort_heap(RandomAccessIterator first, RandomAccessIterator last,
               StrictWeakOrdering comp);

Description

Sort_heap turns a heap [1] [first, last) into a sorted range. Note that this is not a stable sort: the relative order of equivalent elements is not guaranteed to be preserved.

The two versions of sort_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.

Definition

Declared in algo.h. The implementation is in heap.h.

Requirements on types

For the first version, the one that takes two arguments:

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, the one that takes three arguments:

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

For the first version, the one that takes two arguments:

[first, last) is a valid range.
[first, last) is a heap. That is, is_heap(first, last) is true.

For the second version, the one that takes three arguments:

[first, last) is a valid range.
[first, last) is a heap. That is, is_heap(first, last, comp) is true.

Complexity

At most N * log(N) comparisons, where N is last - first.

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 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.