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
Defined in the standard header algorithm, and in the nonstandard
backwardcompatibility header algo.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.
See also
push_heap, pop_heap, make_heap, is_heap, sort,
stable_sort,
partial_sort,
partial_sort_copy
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1999 Silicon Graphics, Inc. All Rights Reserved.
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