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| 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 functors 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 RandomAccessIterator.
-
RandomAccessIterator is mutable.
-
RandomAccessIterator's value type is a model of LessThanComparable.
-
The ordering on objects of
RandomAccessIterator's value type is a strict weak ordering, as defined in the LessThanComparable requirements.
For the second version:
-
RandomAccessIterator is a model of RandomAccessIterator.
-
RandomAccessIterator is mutable.
-
StrictWeakOrdering is a model of StrictWeakOrdering.
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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 RandomAccessIterator [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.
See also
push_heap, pop_heap, sort_heap, sort, is_heap
